I have a standard 454 marine 330 hp 1990. I am trying to figure out which cam to use. I figure someone on this site has used either one of these. I am looking at a comp cams xm270h vs xm278h. Boat is 20' openbow cruiser. Used mainly for fun family boating. I would like to use the stock short block. Will have 049 mild ported heads with larger valves, performer rpm intake. I would like to use the stock 715 carb. I can't afford headers so my stock / snail riser exhaust will have to do. I am looking for a reliable more than stock motor that will not break the bank. Any of your thoughts would be appreciated.