71 K10 3 speed upgrade issues

[chevytruckguy70]

I bought a 71 K10 rolling chassis, no engine but 3 speed trans attached to the transfer case.

I have a 72 2wd 350/350 c10 I'm taking the body and engine from to complete the truck.

I also have a sm465 4 speed from another 2wd truck.

My original thought was to use the 4 speed, but of course it needs the tail shaft to be converted to fit.

Is it easy to convert the SM465 or the 350 auto to bolt on to the transfer case?

I found a 700R4 out of a 4x4 that's had a GM rebuild done to it but from what see I would an expensive adapter to connect it.

The 3 speed needs to come out, what are my options?

Thanks guys