Can i replace my 3.0 MerCruiser engine with a late 70's OMC 4 cyl without problems?

Hello everyone! Recently bought in 2004 Bayliner 175 br and it has a 3.0 Mercruiser engine that is cracked in several places and has oil in the water. It's not fixable from what I understand. I have an old OMC 4 cylinder engine that came off of a mid-to-late seventies pontoon boat and I was wondering if I put the parts off of my bad engine on the OMC would I be able to use it and will I have any problems fitting everything? Thanks in advance I appreciate it!

Flywheel size and coupler are different between them. 3.0 s changed in 1990 to one piece rear main seal flywheel size got bigger

https://www.michiganmotorz.com/base-marine-engine-1967-current-replacement-p-4531.html

this replacement engine add lays out some of the differences. I think you’d need a pre 1985 coupler to work with smaller diameter flywheel keep old starter on engine to work with smaller diameter flywheel. Strip the rest of the old engine down to long block.

I suspect you also will need a mercruiser intake and exhaust manifold of the correct vintage for the older engine to get the exhaust to line up right with merc components. I would suspect the manifold on the merc engine is cracked as well and ports will be slightly different on older head

get them down on the ground and set them side by side should be able to pice it together

other option is to find a newer 3.0 take out and go back in with something less than 40 years old