The Stovebolt Site Forums The Shop Area Engine Shop Engine swap

The primary problem will be the position of the water pump. 55-up engines have the pump about 3 inches lower on the block and further forward which creates fan clearance problems. There is a conversion adapter available which allows you to mount a 216/early 235 water pump to the later engine that repositions the fan properly. It requires drilling and tapping two holes into the later model block, but that's not difficult to do.

The 54 bellhousing is a bolt-up swap, and the front timing plate can be drilled for the earlier mount if necessary.
Jerry