[mr48chev]

In that truck the V8 should be a direct bolt in swap. You will loose the stomp pedal for the six. You can rig an electric stomp pedal using a tractor floor board starter switch though.

You can use 58 front mounts and move them to the V8 position or a tube crossmember and The mounts for the 70's something bellhousing fit the 58 crossmember. That makes it simple. I had to do some hunting to be sure on the rear mounts but the filling station says it works.

A few wiring changes and new exhaust.

The bad part is that normally you have to pull the old 4 speed out and then put the new one in because the shift towers don't clear the firewall.

There may be some mixing and matcing on the front U joint on the driveshaft.

Personally I would do the engine and trans swap and get it running and driving and then after driving it get the rear axle swap figured out even if the mobile home axle fits and has the right gears you want.

I'm assuming that you have dual rear wheels and a 70's 1 ton rear with decent gears might be better than the MH axle. Searching my 77 on the GM heritage archives says that you could get 3.73 gears on a 1 ton.