I also can go with a 383 and build that super cheap to

Ls motors will do just fine in a boat, Volvo is betting that they don't need the BBC an they have ls motors coming out, they have been used in ski boats and big cruisers for years, merc has the stern drive market locked so that's the only reason why they are not in more stern drives, crusader has had them out for years, the engine coupler is the same. With the power you want I would have no problem running the crusader manifolds, they cost less than 1k they appear to flow well, (they are heavy though) and ls motors will make that power through stock car manifolds, look at the Lsa motors they barely pick power with headers. The stock internals will be fine at that power, I would just run a larger gap on the rings, and a cam with decent split to let the exhaust flow, the intake number will be fairly small to keep the torque up and reversion down, look at the lingenfelter cams they are designed with low overlap, they keep the torque up and they work well with superchargers. Search the skater 24 with bravos and twin 5.3l running 104+ with stock junk yard engines through crusader manifolds, or the phantom 21 that runs 96 with a worked ls2/ls3

An LS1 swap is fine. As with any up and coming swap idea, it costs money because the aftermarket support isn't there. You CAN do it. You can just do a 500HP big block chevy for cheaper. You have the parts, you have access, etc, etc, trust me and the guys on this board, right here right now, a 500hp bbc is cheaper than a 500hp LSX. PSIRacing on this board has an Eliminator (I think) with a 2JZ supra motor. It's probably the only one in the states, but that didn't stop him. So where there's a will, there's a way. A naturally aspirated BBC is just cheaper, more reliable, etc. That's all the guys are saying. Like mentioned above, volvo and other companies are coming out with LSX based marine power plants, so the after market will follow. Just my $.02

Thanks everyone for the advice it all helps I just don't know where to start is all cuz there a tone of options to go and I just have a good friend that knows and deals with sbc all the time

you dont really need a blower to get 500 hp out of an ls do you???

More hp but that's running 7lbs of boast and zo6 cam and it gives u 540

550hp is possible with 6.0l with ls3 heads and a cam. (its going to be healthy cam but not too crazy. or 408 with a small cam.

403 LS2 hand ported LS2 243 heads cam headers fast manifold is right at 500whp so thats like 575 thru a manual trans.
http://www.youtube.com/watch?v=fPvVm...feature=relmfu

I would do a 6.0 or 6.2 liter build, I built a Lq9 6.0 build with a carb conversion. dynoed @ 520 hp

I have a set of the crusader manifolds and they look like they flow better than any of the bbc manifolds I have seen, divided runners up the collector, I didn't buy elbows so I can comment on they flow. But it would be fairly easy to fab up tubular elbows like the guy with skater 24 did. I can't imagine that there is too much of a gain with headers. (especially with the cams that are likley to be used in marine engine) A 500hp marine ls should really be no more than a 6.0l a smallish cam, and valve springs. It really is that simple. GM built nice motors then stuffed them with tiny cams to keep the power down.