I'm running the Fel Pro MLS for the last three seasons. 8 lbs boost. No issues.

The engine has to come out anyway. You should put it on a dyno when it's completed and tune for correct air fuel ratio.

ditto

....and ditto

The gasket is not the problem. Keep looking. And get studs to hold the heads on.

Dynoed at 760hp, fuel to air mixture i believe he said was 13:1? Bolts not studs, did not use new head bolts? 6.5 lbs boost, 871 bds, too much? 9 psi fuel pressure at idle, mechanical pump, did not change, weak? use 93 octane, not enough?

If afr is 13:1 that is too lean for a blower motor. Most run in the 11.3:1 to 11.8:1 to keep from detonationing apart. You better find out for sure.

I would say your AF needs to be under 12.0 to make the engines live long and happy.
What is the static comp ratio????? It needs to be less than about 8.75 with 6.5-7# of boost to safely run 93 octane fuel.

Intercooler? Fuel pressure needs to be measured at carb at wide open. 6-7lbs. wot is ok. Do some searches here on detonation and supercharged engines, lots of info available.

the MLS gaskets have a very touchy torque sequence . as well as needing to be retorqued after break in . I sold and ren fel pro performance gasket for 15 years and had no problems and the MLS gaskets are top notch . I chose to run the standard marine/performance series gaskets and im seeing around 7.5 lbs of boost with no problems yet . sounds like a lean burn or possibly failure if they didn't get retorqued after running