The only Mercruiser 4cyl in that hp range is the model 470. It is a Mercruiser designed and cast aluminum engine block with a 460 Ford cyl head. It has been out of production for over 20 years now.
IThey had several troublesome issues.
The riser gaskets can fail, and the manifold also has issues with core shift. Both can cause anti-freeze to enter the engine oil and contaminate it causing engine damage
It is an old technology engine, very noisy and less than desireable in my humble oppinion.
Good luck in your decision.
Thank you verry much that info. helped me make a very important decision.