Supermx, what I would recommend on your setup (460" with B&M 250), is backing the boost down a tad from 9lbs. That's a lot of boost for such a small blower. Tons of heat, combined with a lean AFR and single carb, which ultimately led to your melted piston, and more than likely, torched your head gasket between the cylinders. The best gaskets in the world wont do well with detonation and pistons melting. Many many guys are running MLS headgaskets with more boost and no issues. Heck, my buddy was running 14lbs of procharged boost with standard fel pro marine composite gaskets. They looked new when we disassembled them! (although MLS going back in its place this time). You've got the right stuff, head studs, etc, I believe the tune killed it.

I don't feel o-ringing or any other trick stuff is needed other than a MLS gasket with proper RA finish on a 700-750hp big block.

I have also had good luck with Victor Reinz solicor gaskets on my engines. They were in my engines with the little blowers making 7psi for about 6-7 seasons, and also looked new when I disassembled.

Yes i know my setup was on the limit side and not ideal to be safer with detonation. I will retry mls gasket for this year, and i will pay more attention on detonation, i will control them with a knock monitor for now.