engine differences
 

How can you visually tell if you have 420s 365s or 330s. 1987 to 1999 era

420 has Crane gold rockers and finned cast aluminum valve covers. gill or merc hi-performance exhaust manifolds with stainless steel tail pipes.

365 has stamped rockers. Regular Merc center riser exhaust manifolds. I think the 365 has stamped steel valve covers.

330 looks alot like the 365 from the outside. The intake is lower and the carb is different but the 330 had oval port heads - not the new peanut ports though.

Thats what I remember, others can add.