To catch everyone up: we are replacing the dead Crusaders with MerCruiser 6.8 Magnum. They were an exact fit in all respects, mating up to our rebuilt Warner trannies perfectly. Work is being done by Action Master - they're super!
The load path was through the fly bridge deck, ultimately an 8' by 8' cut. The size of the cut came from chasing core rot, though. i'll post details of that repair later on.
It's been terrific having access to the engine room nooks and crannies to be able to clean and paint; getting rid of 35+ years of crud, corruption, and filth been its own reward. Rewiring, plumbing and general modernization has been expensive, but worth it.
Best to all,