502 lifter noise

Have a 03 502 330 hp crate motor in a 18 ft jet come in for a no start. Found bad fuel pump and starter, replaced with marine parts, started up no problem but has terrible valve noise. Pulled valve covers and found non adjustable rockers. I have no history on engine, has 60 lbs oil psi and 180 compression. My question is this a common problem with this generation engine? If so is the fix lifter replacement or converting to adjustable rockers? Also has electric fuel pump with oil shut down, can I use the by pass connection on starter to turn on fuel pump when cranking? Seems strange not to have pump on when cranking and have to wait for oil psi. Any ideas on what oil viscosity to run since I want to change oil due to owner not knowing. Yes I know this isn't a Mercruiser question but Mercruiser runs this gen engine in some applications. Thanks for any help,Guppy

I suggest you see if there's any valve lash slack by hand cranking her over and feeler gaging a few valves--there shouldn't be much. If this is the case, it "sounds like" (pun) somebody didn't change the oil often enough. If so, that and a bottle of Lucas oil stabilizer will get rid of the noise.

Jeff

PS: These are not normally clanky engines.

Thanks for the reply Jeff. Did some research in some chevy hot rod forums and found out these motors have a habit of wearing rockers out if ran steady at upper rpms, above 4grand. Reason why they run props and not jets with this engine. There is a conversion kit made to swap in adjustable or full roller rockers for this engine. Reason why the hi-po version from GM have this set up.Now up to owner to see how much $ he wants to spend.

Good research!

Jeff