3.0 l engine swap 1977 fairline holiday

hi guys, i hauled the 3.0 l motor out of the boat last week and it is toast. the cylinder walls are so thin that there is a small hole near the top on # 2. there was water in this cylinder and it also blew out the head gasket in the same area. m6y question is, can i put a different engine on to this drive, like a straight 6 (175 hp).. i got the boat 4 years ago but i am unsure if it is the original engine. i know that the upper gearcase in my drive was rebuilt a couple of years ago and the guy ordered a new shaft that was almost $500 and said something about the profile of it. he said that he ordered one for the 3.0 l but ended up being the wrong profile. is it possible that someone over the years swapped out a 6 for a 4 cylinder. how do i know if my drive is compatible for a 6 or is it a different drive completely? any help would be greatly appreciated.

thank you and safe boating

What manual you working out of.

Electric shift stringers had a high profile. And a low profile.

All that really means is a stretched version for the high profile, used longer water pump shaft.

To the question of going from say 140 hp to say 165 chvy straight six be careful not any ole straight six will do.

Marine and some auto ones need the boss, on the front of the motor.

In the pm you will have in a minute will explain it all.