What head gasket for boost? MLS leaking oil

The Cometics are the best solution. Thickness is set by the compression ratio that you want and any quench gap you want. Are your pistons 'down in the hole"? I.e., is there some height to the deck from the top edges of the pistons at TDC? With a stock Magnum bottom end, there should be. In that case, there is no quench gap to set and so you use the Cometic thickness just to set static CR. And the static CR needs to be computed so that with the 10 psi boost you don't over do the overall cylinder pressure.

Hmmmmm. It just occurred to me that your static CR might be too high to start with. That would explain the head gaskets going and the detonation. With the stock Magnum bottom end and 63 cc head chambers and the thin .025" head gaskets, it looks like you had a static CR of around 9.0 or 9.1. Okaaaay, I think THAT might be the problem. Your cam looks to be for pressurized engines (wide LSA) but I suspect the resulting dynamic CR of around 7.4 is still too much for 10 psi boost. Detonation will result and the head gaskets will keep going.. if not worse. Maybe it is fortunate that your head gaskets weren't clamped down hard, as they could blow rather than a piston top or ring or ring land! (Dang... maybe this thing DOES need to come apart... for inspection of the rings....)

I suspect that the static CR needs to be brought down to the low 8:1 range to be OK with 10 psi boost. It's gonna take a lot thicker gasket than any discussed so far. I can do some research but it will take me some time to get to the data.

Can you post a pix of the piston tops so we can all be sure what pistons you have? (There are a few Magnum piston tops....) Then a clear picture of the static CR can be had. Ideally, you would also give us a measurement of how far the top edge of the piston is down from the deck with the piston at TDC, so we can be sure.