Re: carb issues
Yes! there is major safety considerations that a marine carb has, but auto does not! Any carb in an I/O must be CG approved. While there is not allot of differences, it is critical to use a marine carb to prevent explosions within the confined space around an I/O. The main difference is fuel bowl venting. All venting must be directed down the barrels of the carb. If you look at a Holley marine vs auto carb, you will notice the prominent J tube vents on the marine version. There are also bushings, attachment place for fuel pump failure vent, accelerator pump seal, and other small changes to prevent/reduce chance of fuel dripping external. There are also non-safety differences, including the reduced vacuum line attachments, such as corrosion protection, and marine is jetted significantly richer than auto.
It is a real threat of explosion, and after the investigation all liability will be dropped in your lap - if you survived! Outside of that, you can get stiff fines from spot inspections on the lake. They probably will make you get towed, vs letting you drive back to ramp. Research through the I/O forum, every year there are numerous discussions on this.
Now back to your mod. I have seen a few posts of Ford 302 upgrading to 4brl. You will get some hp increase, but it isn't allot. You are probably talking only a 2-3mph wot improvement. If you are raw water cooled, and boat in salt or brackish water, finding a cast-iron manifold maybe somewhat difficult. If aluminum, you would need a marine specific (bronze water passages) and don't know of any being produced for the Ford 302.
