My boat has a stock 350 mag (carb engine) and I'm looking to do some upgrades. I have a chance to buy some fully dressed GM Aluminum Fast burn heads at a killer price. I built the engine in my last boat so I have some experience with iron vortec heads and the lt4 hot cam kit, killed two outdrives with that combo. My current boat runs out at about 58 mph. I really don't have a speed goal set because all those do is set you up for disappointment. That being said my plan is to use the stock short block, fast burn head, new intake and carb (not sure if 650 or 750 would be better), stainless marine manifolds, and some form of mild cam to add a touch more punch to it. Not looking for max horsepower or speed, going for fun and reliable. The zz4 cam is tempting as it is a touch more mellow than the lt4 cam. I'm also going to be looking into some of the comp cams marine grinds as well.

vortec heads are a great upgrade from std heads, but require matching intake and longer plugs, I think the fast burn heads are close but aluminum, but without closed cooling be careful, even in not salt water they corrode badly

We used the Fast Burn heads in an engine design class. was a competition, and started with two 350hp 350 cu in fast burn crate motors. We had a $500 budget to get the most average power (basically engine master rules) below 6500. One motor made 426 hp and another 452 hp on pump gas. Ports were cleaned up and massaged, heads milled a bit for some compression around 10:1, and cam swaps.

I wouldn't hesitate to use them.

At lower rpms (5500ish) and compression (9.5ish) you see in marine engines, I think the smaller runner of the vortec head would be better, especially if you are looking at a cam smaller than the LT4 hot cam, and they are cheaper.

Edit: Just noticed you can get them for a real good price, if that's the case why not try them.