How do you convert a small block to a big block motor in a 1970 Chevy truck?

It sounds like you want to know how to change the engine in a 1970 Chevy truck from a small block to a big block.

If that is the case; there is no difference in the mounting of the engine to the transmission or motor mounts.

The exhaust system will need to be changed, and the small block radiator might not be big enough to handle the extra heat made by a big block when it's being worked. (such as on a hot day or pulling a heavy load)