Why do you want the 4 speed? A 420/465 will get you a great granny gear for off-road, but you'll still drive it on the street like a three speed.
If you're looking for driveability, get a Cruiser 4 speed.
This is true, but....
I have 8 years of experience driving an FJ40 with an SM420. It is indeed a 3 speed plus a granny first. If you do any 4 wheeling at all, this tranny will improve your capabilities more than anything else you can do for the same $$. I also have a 465 partially torn down in the garage for comparison.
The basics:
SM420 1st gear 7:1
SM465 1st gear 6.55:1
H42 (Common USA LC 4 speed) 1st gear 3.5:1
H41 (Uncommon in US) 1st gear 5:1
A couple of comments:
The SM420 second gear, is about the same as an H42 first gear, so starting from a stop on the street, is no big deal. Both 420 and 465 are not syncronized in 1st gear, so you must be at a complete stop to shift into 1st.
There is a wide spread in SM420 between 3rd and 4th, which in a Land Cruiser, with the narrow rev range of the motor, can at times be a pain. With that said, I've traveled all over the Sierras in mine. Some of the long grades I do at 35 MPH in 3rd.
Both the SM420 and SM465 are better built and far stronger than Land Cruiser 4 speeds. Both were used in up to 2 1/2 ton trucks. The gears are huge in comparison to the H42. The price you pay for all that massive gearing is that it is heavy and shifts slowly.
THe advantages of the SM420 are that it's shorter(2 inches) and lighter(125lbs vs 175 lbs) than an SM465. It still is significantly heavier than Cruiser 4 speed(75 pounds roughly). It's true you will need a Chevy bellhousing but these are a dime a dozen in a yard. If you go with SM420 you need the older style with the smaller hole for the front bearing retainer.
SM420s almost all came with the 10 spline output, which is what you need to adapt to Cruiser 3 speed transfer. Only a small minority of 465s come with a 10 spline output, and many of those are boogered up-for some reason the 10 spline outputs get damaged in routine use, so check carefully before you buy or just get a new main shaft. Most SM465s will have a 35 spline shaft. Now I believe I saw that AA had an adapter for SM465 35 spline to Land Cruiser 19 spline split case. That would not be a bad combo.
The SM465 does appear to be even heavier duty than the SM420, but it weighs 50 pounds more. I can't pick it up by myself. It seriously was Gm at it's best. Not a big deal, just remember it's a beast and don't hurt your back fawking with it.
On balance, I believe the SM465 is a
slightly better choice for 1 reason: it doesn't have the reverse hump in the way of your front drive output, but the SM420 is a fine choice that works great with the bonus of an even lower 1st gear. Get which ever one is most available.
If this is going in an FJ40, I strongly recommend you use a "plate style" adapter. The Advanced adapter unit adds significant length, which is OK in a wagon but in a SWB 40 you don't have much room to play with it.
So if you want to keep your existing transfer case, either the 420 or 465 is a great choice. If your truck is mostly a pavement pounder, stick with a Cruiser 4 speed. For a while OrangeFJ45 had an H41 + split case that was prepped and ready to go at a good price. That's almost the best of both worlds with the 5:1 low and the strength of the split case. It would be a bit more money, and you might need a different bellhousing/adapter but it would be awesome. If you have a bit of available cash, call Georg at Valley Hybrids and grab that unit before I do.
Good luck, there are really no "bad" choices here. How much do you want to spend?
