I have small peanut port heads on my cruiser. Sundancer 290. The heads are 10114156 and 118cc open chamber. I'm getting ready to put my block together and came across some 279 Vortec heads. 99cc closed chamber. I'm trying to decide if the swap is worthwhile or not. $200 for the new used heads that I'll go through myself. The extra compression won't be an issue for the stock cam grind right? I'd like to leave the long block stock. I was able to reuse the crank, rods, pistons and cam.

Might want to upgrade intake as well.

I would have, but I bought a new OE cast one already. I'm not looking for too much being a cruiser. I figured bumping up the compression a point and better flowing heads for $200 would be money well spent.

The Vortec flows a LITTLE more than the peanut. The main benefit us the 99cc heart-shaped combustion chamber. You will see a full number bump in compression. Along with that bump, you should add some cam to it and make sure your springs are matched. You can probably find a stock 454/502 MAG MPI roller cam from somebody here pretty cheap (your Gen 6 block should have a roller in it already. But it will be on the small side). The added compression will love a little more duration. Don't go nuts with the cam - your Gen6 flat top pistons won't accommodate more than 520 lift without deeper notches depending on duration.

I did end up picking up the 279 heads and will use them. Like you said, for the 99cc chamber more than anything.
I've heard the same thing that you said about lift, but I have 279 heads on my 454ci +.030" in my 69 Camaro. I'm running a Lunati cam with 241/249 @ .050" 625/625 and 110 lsa. 2.19/1.72 valves. Stock pistons, not fly cut and heads shaved .020". I built it myself.
My stock boat cam is completely anemic. I'd love to find a better cam for short money, but I want to keep it cruiser/heavy load not high performance or race boat grind.

How about used 454mpi / 502 mpi cams ?
Thousands have probably been taken out.
The 454’s made 385hp and mild enough to use stock exhaust manifolds, and go thousand hrs or such with no valve train issues.

Mercruiser 454 502 Mag Roller
Merc# 431-850478 / GM#12551622
.004 300*/ 300*
.006 288*/288*
.050” 224*/224*
.200” 125*/125*
Lift .483”/. 483”
ICL 109*
LSA 115.5*

I actually had that cam in my notes to think about. It seems like it would be a good bump up from what I pulled out.

Merc# 431-850453T / GM#12552296
.004” 280º/299º
.006” 266º/284º
.050” 204º/209º
.200” 113º/114º
Lift .480”/. 483”
ICL 115.5º
ECL 120.5º
LSA 118º

Lol. You must have found that cam info from me back in time. Glad it helps. :thunbs

Good possibility. I remember searching around for the info for the higher hp/tq factory cams. Your info has helped me before and I'm sure will again.
Now the trick will be to find the cam. Did a quick search and all I found was the triple priced new Mercruiser listings.

Do a ‘wanted ‘ thread. There is a section in the forum for it.

502mpi one of the nost modded Merc motor ever. So decent chance there are cams around.