Your mechanic is getting ready to get you in trouble. If it is as mentioned an 8 lug 3/4 ton, then it should be open driveshaft and not quite as big a deal to "transplant" a V8 into. If it is a 3100 half ton, it will have a torque tube driveshaft which means the swap would also include a different transmission, driveshaft, rear end, and leaf springs. I think your budd has good intentions but is trying to make your truck more into something he would like steering you more towards the street rod direction. A 54 engine should have insert style bearings and an oil pump. In the old days, they would rebuild those things in the "field" leaving the block in the engine bay. The right way is to pull it and do a good rebuild, or even find another known good engine of similar year. TX should be full of them.
