Hate to resurrect an old thread, but just had to reply and also ask a question or two.
Just a disclaimer: before I went into electronics & then later software, I was a machinery tech (mostly diesel ICEs - first in the military, later working summers as at JD dealers while going to college on the GI bill). Before the military, I worked off and on as a mech and other jobs. My point is, I do understand
Diesels vs. gasoline. If you throw out any electronics (especially computers), then IMO, diesels still win for a JIC/SHTF/backcountry rig for several reasons:
Simpler in concept; as long as you have fuel, compression and oil pressure - the diesel will keep running - so much so that you have to literally kill the engine by shutting off its fuel delivery (and sometimes even then, if the engine has run away, you need to at least try to strangle its air source).
Generally two of those three things are not the problem when a gasoline engine stops running (or runs so bad it is useless); it is either fuel mixture (carbs can be stubbornly finicky, especially with water crossings) or it is ignition (which can be fragile). More so if you throw electronics into the mix.
If the alternator rectifier blows a diode, count the hours before your gasoline engine no longer has the battery current to keep the ignition firing. For a properly setup diesel (replace the fuel shutoff solenoid with a cable) and the engine will keep running until it is out of fuel (assuming you have a mechanical fuel pump - my Dodge Cummins does, my Hilux does not - but I could rig a gravity feed system without too much hassle - I've done it before with a Datsun when there was water in the gasoline and the fuel line froze while on a mountain ski trip).
So, my philosophy for SHTF/backcountry vehicles is to keep them as simple as possible, and easy to repair (if possible) without having to deal with additional variables and preferably without electronics (especially computers). An all mechanical diesel helps in that regard. Other things like replacing/swapping out stuff like assisted axle engagement (like on my '98 Hilux and my '97 Dodge truck) with manual hubs will simplify things at the cost of convenience.
Same with replacing a solenoid/whatever to shut off fuel with a cable that does it manually. I am also thinking of using manually engaged lockers instead of air engaged lockers, or e-lockers or LSDs etc. - again, to simplify things.
With regards to the fact that Toyota diesel engines are fairly rare in the USA compared to their gasoline counterparts - yes, that is an issue. In a backcountry/overlanding situation, you generally are not going to be finding a parts store in the middle of nowhere anyway.
Regardless of location, if you throw a rod, wipe a bearing, swallow a valve, etc. - you are going to be tearing down either engine anyway, and it probably won't be the case that you can do an overnight fix for either engine.
Water pump? Ok - stock a spare (only $170), just like you probably would for a gas engine. Same with belts and hoses. I would probably also stock a spare alternator so that I have power brakes (the pump on the back of the alternator) - otherwise charging the battery can be done with solar panels or an external generator - maybe run the electric fuel pump on my Hilux.
Both my Dodge and my Hilux have manual transmissions. Low battery? Defunct starter? I can roll/push/pull the vehicle, pop the clutch and bump start the engine. Can do that with an auto-trans (at least not most of them currently made) and most automatics now have electronics in them. Which reminds me - preppers/et. al. worry way too much about EMP disabling their electronics - way overblown and an overused trope in PAW fiction. That said, reducing your dependence on electronics in what can be a crucial survival machine, is a good policy.
SHTF vehicles are not just for preppers; a dependable/reliable transport machine capable of traversing rough terrain can be important for most anybody, whether you are into self-reliance or not. People in the western USA have had to "bug out" (evacuate) from their homes due to forest fires. I personally had to evacuate, with 15 minutes notice, from my mountain home, 6 years ago on Labor Day weekend due to a human caused forest fire (fortunately, the local fire fighters prevented the fire from reaching my home - but it was only a mile away).
There are also wind storms, floods, even volcanoes and earthquakes/tsunamis (each of these are not uncommon on the west coast).
Which segues to another aspect of having an overlanding/camping vehicle; they can serve as a backup shelter.
All that said, my daily driver - a '14 BMW X1 AWD SUV - is gasoline fueled, has multiple computers controlling almost everything. I really like it and it has been fairly reliable (except the times it locked me inside the car because of an electronics short in the "comfort access" doors - which I have since had fixed).
My kids Audi Q5 has proved supremely unreliable - every year they spend several thousand $ fixing some computer/electronic fault, and it has more than once stranded them (and me once) requiring a tow, and often days if not weeks in the repair shop (where is it now as I type this). Could I fix it? Maybe, I not only have mechanical training/experience, I also have a EE degree and I made a career from programming computers, so I understand the basics. But I don't have the diagnostic equipment (at a least not the really good stuff the specialists have in their shops), and I don't have their experience with today's German cars - so it would be an iffy thing, and I don't have the parts either (nor would it make financial sense to have spares because the electronics modules are expensive).
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So, I am interested in what the OP wound up with as a vehicle?