Short answer: Older Toyota diesels are a bad (expensive and underpowered) choice compared to practically any engine in the last 25yrs. A 5.9L Cummins is a bit heavy and overkill unless you plan on towing a big trailer, but common and relatively cheap. I would recommend 2010ish 2L VW 4cylinder at this point if you can make it work.
Long answer:
80s-90s Toyota diesels - Even if it magically appeared in your engine bay at no cost to you, all you would really gain over the 2F/3F would be a little fuel economy and some diesel noise. Anything before the 12HT would be drop in power compared to a 3F. The big downside would be scarcity and high cost of parts when you had to fix anything. The power/weight and overall efficiency is pretty bad. If you're willing to consider non-toyota engines, then I don't think you're the type of crazy to bother with an old toyota diesel swap.
4BT Cummins- Robust, but terrible power/weight and relatively expensive. Since its a 4 cylinder version of the 6BT, its hyped up as a good choice for a 'small diesel swap'. The hype and rarity have caused the price of them to be absurdly high. That is all pretty silly since its still 3.9L and weighs ~750lbs, ~150lbs more than the factory 2F/3F and similar weight to an old Toyota 6 cylinder diesel. Noise and vibration are bad, worse than other diesels. ~1500rpm drivable rev range leaves something to be desired for driveability. You add ~150lb of engine weight, a huge amount of noise/vibration, and cut your usable rpm in half. The plus side is an extra 100-200lb-ft of torque and 10-25% better MPG. Its 2020 and there are much better options. An overpriced, heavy, noisy 40yr old tech seems like a silly choice. I guess if you enjoy driving an old tractor and you happen to have a 4BT that you're not allowed to sell to some other poor sap....., then sure go for it.
5.9 Cummins 12v or 24v- Cheaper than a 4BT due to being exponentially more common. Unbeatable parts availability, OEM and aftermarket. 6cyl runs smoother and revs a bit higher so it's a bit more driveable. The large displacement gives you an easy +200hp/+400lbft even on a tired old 12v. The thorough aftermarket support allows you to easily make 5 times that if you really wanted. Its a great choice if you plan on installing 1ton axles and hauling a trailer/boat. Quite heavy if you're aiming for a lighter camping rig. Though we're talking 750lb vs 1100lb, 4BT vs 6BT, so they're both heavy. 2F/3F supposedly weigh ~600lb. I would never do a 4BT over 6cylinder Cummins. For cost and availibilty, the 5.9 is great option for a swap. Do engine+trans+axles and be done with it. Might be heavy and noisy, but its a diesel...they're heavy and noisy. It'll be beefy and parts will be relatively cheap. Big body FJ60 isnt really ever going to be a lightweight wheeler anyway. Probably could sell the old Toyota parts and make up a good portion of the expenses.
R2.8 Cummins - Expensive and only 160HP / 310lb-ft, but a little quieter than older diesels due to the modern injection system. Not a bad choice if you have the money and want a Cummins in your rig. Quite dissapointing that an expensive diesel engine designed in ~2015 doesnt come with a VNT turbo and is easily matched by a 2010 2L VW TDI.
There are quite a few companies out there now making adapter kits for various combinations of common diesel engines (VW, Mercedes) with common transmissions. For a simple wheeling/camping rig, I would chose something along those lines.
After spending way too much time and money on my Mercedes OM606 swap it works great, but I cant say that I would recommend it in 2020 unless you specifically want a fully mechanical IDI. If you want the best option in terms of power/weight/efficiency/noise/cost, then there are better options out there due to the huge improvements in diesels in the last 20 years. I like my rugged old 60, but installing a more modern engine is a better idea.
If I had to do it over again in 2020 instead of 2014, then I would likely do a 2.0L diesel out of a ~2010ish VW or Audi. They are old enough now to be found used and they have good aftermarket support. With no modifications they have similar HP/TQ as a 3FE, while also being smaller, ~150lbs lighter, and 2x-3x fuel MPG. With a simple plug n play tune they put out 175hp/300lbft (+250hp if you swap in a larger turbo). Plus it would leave plenty of room in the engine bay for big cooling components with room leftover for easier access. The other benefit of the modern direct injection system is that they run quieter, so you don't sound like a tractor that can be heard from a quarter mile away. Even the early 2000s 1.9L VW diesel can be tuned to output 150hp/250lbft.
You could get similar power output from a Toyota 1HD-FT or 12HT, but it would be bigger, heavier, noisier, less efficient, and more expensive.
If you would like a bit more power, then the 6cylinders from 2003+ Mercedes/Dodge can is easily be tuned to put out ~240hp/~400lbft in stock form. Though I haven't seen adapters for them yet. The OM648 is the inline 6 and the OM642 is the V6.
Toyota has made similar improvements to its diesel engines in the last 20 years, but they are not as available in the North American market.
Long answer:
80s-90s Toyota diesels - Even if it magically appeared in your engine bay at no cost to you, all you would really gain over the 2F/3F would be a little fuel economy and some diesel noise. Anything before the 12HT would be drop in power compared to a 3F. The big downside would be scarcity and high cost of parts when you had to fix anything. The power/weight and overall efficiency is pretty bad. If you're willing to consider non-toyota engines, then I don't think you're the type of crazy to bother with an old toyota diesel swap.
4BT Cummins- Robust, but terrible power/weight and relatively expensive. Since its a 4 cylinder version of the 6BT, its hyped up as a good choice for a 'small diesel swap'. The hype and rarity have caused the price of them to be absurdly high. That is all pretty silly since its still 3.9L and weighs ~750lbs, ~150lbs more than the factory 2F/3F and similar weight to an old Toyota 6 cylinder diesel. Noise and vibration are bad, worse than other diesels. ~1500rpm drivable rev range leaves something to be desired for driveability. You add ~150lb of engine weight, a huge amount of noise/vibration, and cut your usable rpm in half. The plus side is an extra 100-200lb-ft of torque and 10-25% better MPG. Its 2020 and there are much better options. An overpriced, heavy, noisy 40yr old tech seems like a silly choice. I guess if you enjoy driving an old tractor and you happen to have a 4BT that you're not allowed to sell to some other poor sap....., then sure go for it.
5.9 Cummins 12v or 24v- Cheaper than a 4BT due to being exponentially more common. Unbeatable parts availability, OEM and aftermarket. 6cyl runs smoother and revs a bit higher so it's a bit more driveable. The large displacement gives you an easy +200hp/+400lbft even on a tired old 12v. The thorough aftermarket support allows you to easily make 5 times that if you really wanted. Its a great choice if you plan on installing 1ton axles and hauling a trailer/boat. Quite heavy if you're aiming for a lighter camping rig. Though we're talking 750lb vs 1100lb, 4BT vs 6BT, so they're both heavy. 2F/3F supposedly weigh ~600lb. I would never do a 4BT over 6cylinder Cummins. For cost and availibilty, the 5.9 is great option for a swap. Do engine+trans+axles and be done with it. Might be heavy and noisy, but its a diesel...they're heavy and noisy. It'll be beefy and parts will be relatively cheap. Big body FJ60 isnt really ever going to be a lightweight wheeler anyway. Probably could sell the old Toyota parts and make up a good portion of the expenses.
R2.8 Cummins - Expensive and only 160HP / 310lb-ft, but a little quieter than older diesels due to the modern injection system. Not a bad choice if you have the money and want a Cummins in your rig. Quite dissapointing that an expensive diesel engine designed in ~2015 doesnt come with a VNT turbo and is easily matched by a 2010 2L VW TDI.
There are quite a few companies out there now making adapter kits for various combinations of common diesel engines (VW, Mercedes) with common transmissions. For a simple wheeling/camping rig, I would chose something along those lines.
After spending way too much time and money on my Mercedes OM606 swap it works great, but I cant say that I would recommend it in 2020 unless you specifically want a fully mechanical IDI. If you want the best option in terms of power/weight/efficiency/noise/cost, then there are better options out there due to the huge improvements in diesels in the last 20 years. I like my rugged old 60, but installing a more modern engine is a better idea.
If I had to do it over again in 2020 instead of 2014, then I would likely do a 2.0L diesel out of a ~2010ish VW or Audi. They are old enough now to be found used and they have good aftermarket support. With no modifications they have similar HP/TQ as a 3FE, while also being smaller, ~150lbs lighter, and 2x-3x fuel MPG. With a simple plug n play tune they put out 175hp/300lbft (+250hp if you swap in a larger turbo). Plus it would leave plenty of room in the engine bay for big cooling components with room leftover for easier access. The other benefit of the modern direct injection system is that they run quieter, so you don't sound like a tractor that can be heard from a quarter mile away. Even the early 2000s 1.9L VW diesel can be tuned to output 150hp/250lbft.
You could get similar power output from a Toyota 1HD-FT or 12HT, but it would be bigger, heavier, noisier, less efficient, and more expensive.
If you would like a bit more power, then the 6cylinders from 2003+ Mercedes/Dodge can is easily be tuned to put out ~240hp/~400lbft in stock form. Though I haven't seen adapters for them yet. The OM648 is the inline 6 and the OM642 is the V6.
Toyota has made similar improvements to its diesel engines in the last 20 years, but they are not as available in the North American market.
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