lowering a 383 into A-body

I think he's trying to say that having the rear end of the car up on ramps/stands will make it easier because the engine/transmission will not need to be on a steep entry angle in order to get into the engine bay. Then, once it's in the bay, the rear end can be lowered and the engine/tranny will line up with the mounts.
This will also minimize fluid loss through the rear seal of the tranny, if that's an issue on your assembly.