GM dual plane that came with the ZZ502. Not sure but I think it's manufactured by Edelbrock.

Gen 6 heads will loose the exhaust seat if they get hot. The press on the seat is only about .002. I had some fall out and the machine shop put in new ones that were oversized with .004 press fit. Make sure the shop does not do a small 3 angle valve job. You want at least .080 seat on the intake and .100 on the exhaust. A little bigger is even better.

BTW, Teague has mentioned many times with GM Gen VI heads to replace the seat if you are going to reuse.

The Dart Iron Eagle is a good casting that is cheap. Flow as good as the aluminum head.

That 110 cam is a poor choice for a boat engine. Not really enough in my opinion. A Crane 230/236 at .050 (HP 500EFI) is a much better choice. A step up.

A dual plane manifold is marginal.

If your Holley was square jetted, you must have power valves in the front & rear. At idle, hook up a vacuum gauge. Whatever the average vacuum is, go down at least 2-3 power valve sizes. Say your vacuum at idle is 7. I would use 4.5 PV. If it is 5 you would need 2.5.

Generally you move all 4 jets the same. Maybe go up 2 more sizes in the rear for a little extra fuel on top.

Look at the metering blocks. If all 4 brass plugs are level at the top you do not have high flow metering blocks. If two are deeper down, then you are good.

Most shops bore out the rears, remove the power valve from the rear, and go up 8 jet sizes, which equal square jetting again. A PV adds about 8 jett sizes.

Lean is hot.

Sorry & good luck

Linster: The metering blocks I believe are high flow based on what you indicated. 2 of the plugs are twice as deep as the other 2.
Why do most shops bore out the rears and remove the rear power valve? What is the advantange to this as opposed to square jetting?