Are rockers on newer 454s adjustable?
 

I have the mid 90s Lo-Po 310/454 , it has the external fuelpump (no pump boss) and the newer valve covers and peanut port heads. I havent used the boat in 5-6 months,today I fired her up and the rockers were noisy, I figured the lifters had pumped down so i let it idle a while (oil pressure was as strong as always) and took it for a ride, power seems to be the same but the rockers are definately louder than before. As far as I know these arent adjustable but I may be wrong so if I am let me know!
On the same track if you add older ovalport heads and roller rockers to these engines do you have to use different length pushrods or are the stock length fine.
Thanks!

The rockers are non-adjustable. You can swap in an adjustable stud very easily. I'd be concerned about the sudden appearance of this noise. It's possible that one or more of your lifters has "stuck" during storage. This can result in serious damage if not addressed. I would pull the valve covers & intake and then the rockers & pushrods. Pull each lifter one at a time and measure the distance from the pushrod cup seat to the top of the lifter body. If one or more is lower, I'd consider replacing them.

Your engine is probably a Gen V and has 088 heads on it- they're pretty good. I'd leave them there. If you have to take the exhaust off to do this work, I'd consider pulling the heads & freshening them up- Marine valve springs are a weak area anyway.