Can you help me identify this engine?

[schwim]

The boat is a 1991 Chaparral 1800SL It's been sitting for years. I'm pretty sure the engine is going to be junk(it sounded like a diesel when I heard it run, tons of knocking) but I'd like to know what it is so I can research either parts or swappable replacement engines. I don't see any model designators on the engine but I might be missing them.
Any help Identifying would be greatly appreciated. Let me know if there's any better info I should be providing.

 

[Bondo]

Ayuh,...... Welcome Aboard,....... That's a 3.0l Merc motor, probably with an Alpha 1 drive,....

 

[schwim]

Ayuh,...... Welcome Aboard,....... That's a 3.0l Merc motor, probably with an Alpha 1 drive,....

Thank you very much! I was considering finding an engine to drop in while figuring out if I could rebuild what I have, is this comparable to automobiles where there's only a very limited range of engines that are swappable or is it more standardized?

I'm only familiar with autos, where I've had to use adapter plates, mounts, conversion TCs or clutches and flywheels.