Cruiserdrew
On the way there
All SM420s and SM465s are 4 speeds. It's just that first gear is very low and unsyncronized, so people tend to drive them like 3 speeds. Meaning, only gears 2, 3, and 4 are used in routine use. Thus, "driven like a 3 speed". That first granny gear is extremely useful, particularly in the SM420 where it is 7:1. That is twice as low an a regular H42 Land Cruiser 4 speed, so you get significant gear reduction. I have an original shifter "ball" for the SM420 and it's labled: L, 1,2,3 and R, so clearly GM meant you to drive it as a 3 speed, with a very low granny when extra gearing was needed, like pulling stumps, agricultural work, etc.
The other benefits like,,,bullet proof strength, easy availability etc are all just bonus.
The other bonus' of an SM465 or SM420 to you, are that you already have all the needed important parts, ie the right transfer, the right clutch etc so it's close to a drop in for you. Since you have a SBC, I think you need a GM bellhousing of appropriate vintage.
If you don't go offroad at all, then I agree, the H42 (Standard Land Cruiser 4 speed) is the best possible tranny you could have, unless you decide to swap in an H55f, which is a whole different animal.
