Looking at putting GM ZZ502s (# 12371204) in my boat, but concerned as the GM performance part catalog states "not intended for marine applications." Can these engines be marinized and if so, what needs to be changed?

Do a search on the topic, you can read until midnight.

I've got a zz502 in my 22 Eliminator Daytona and I love it. The biggest thing to watch is the cam it's a 1-10 lobe sep wich can call some big problems other than that not a big deal.

As mentioned other than the cam I don't see any big deal. I haven't read all the threads and post however look at all the 454/330's out there that run forever. There simply a truck / rv engine. Not sure how your going to run it however you may want to consider upgrading the exhaust valves.

if you run dry exhaust it dont matter wt cam in the motor . there is a guy on this site put a 572 gm motor in his boat and has over 300hours on the motor . you can look up his post and see wt he has to say?? good luck

Just a cam is why. I read a whole article abouth this is pbm last year. Water reversion. Dry exhuast as stated or cam swap as stated best of luck.
-Mike

I've got 200 hours on my ZZ and she still strong.

ZZ502 crate motor is a good affordable baseline 500HP package. However, to truely make it last in the marine enviroment, follow the recommendations on your search here at OSO. Your short list:
1) oil by-pass valve
2) plug in oil filter pad
3) oil pan (funny that the first three are oil related)
4) RPM rev limiter
These are the "must do" items. Good luck

The simple fact of this deal is the warranty, crate engines are covered as long as you can produce a vin #, marine engine are NOT warranted thru GM at all..unreal but found out the real deal a while back..all marine engine warranty is thru the outlet where sold...so be carefull there..Rob