Friend selling a 36 ft. Baja Boat has Merlin blocks and Merlin heads. How to tell if they are marine blocks
The original owner has health problems and someone bought boat to help family on health bills, 42 hrs on 468 rebuilds but don't know anything on rebuilds.

A blockis a block so to speak. Track the build sheet down and see what the internals are. That's what you need to know

IIRC Merlin blocks actually had Merlin cast into the front of the block.