would Ls6 heads be good
 

for a marine engine?

I have them on my 509 work fine so far...

you would need to narrow down which heads. there was an LS6 with closed chamber and open chamber. the open heads work pretty well. the closed chamber shroud the valve quite a bit. do you have the casting number for the ones you want to use?

188's I think is the Q here... open chamber.. used on all high perf Mercs since the 70's...#14096188

or if you really mean the 71 LS heads #3994026 spare them and sell to someone who really needs them ...and get DART Merlins...or go with the early (big) Oval port heads and put 2.25/1.88 valves in them and do a pocket porting/bowl work and you'll run circles around rectangular ports.