Thanks Grayscale! It little things like the 60 transmission being longer that sways me against the swap. It was bad enough modifying the driveshafts for the V8 conversion back in the day.Isn't the 60 transmission is (H42) longer than the 40 (H42) version? Like a FJ60 4-speed gearbox has the casting kinda like of the Toyota 5-speed, so it is longer, iirc, and won't be a no-brainer in a 40.
Used transmissions and transfercases should be checked for rust internally, particularly if the transmission has been in a 40 without roof.
In my opinion, a significant end-goal of all of this is getting as long of a driveshaft run as you can from the rear pinion to the transfercase. Reducing the angle (by increasing the driveshaft run) that at the U-joints will minimize driveshaft vibrations at highway cruising speeds. I recall that there was a non-sweet spot around 68mph that my '73 hated with the SM420. It could have been one of a many other issues, but, either way, I failed to resolve it before I sold the truck.
If anyone is looking to test the integrity of their dental work, find a washboard road and stick to 2nd gear (H42) in high-range in an FJ40. I did, and I decided to cancel my appointment that I had for later this month. Plus, I'm a sovereign-adult, and I can clean and inspect my own teeth, than you.