I'v got two mercruiser 7.4L motors in my boat. The intake manifolds are looking pretty rough on the outside. I also happen to have two GM 6269318 aluminum intake manifolds (with marine waterjackets, rectangular ports) never been used. It is a 454 / 502 part. Would these high rise aluminum intakes bolt on with no other modification/tuning to the motor?
Yes. Merc 7.4 and Chevy 454 parts are interchangable. Running in salt on a raw water cooled engine might not be too good for the intake though. Longevity would be an issue.