Hi, New to this site, great info. I would recommend a Holley 830 HP, I believe it is an 80511 # I have this carb on my Hot Rod pickup ( sorry no boat yet ). I love the fact it has drilled throttle plates, it lets you idle a big cam real nice without fouling plugs. The carb is actually designed for Winston cup engines.I used a two inch spacer on a Weiand Stealth for my 472 Ford 50cc pumps 0.040 pump shooter and 3.5 hg power valve.Throttle response is very quick, I purchased it on EBAY new for less than $ 450,It retails for $ 700.