Core/Freeze Plug blow out

OK, if another pops out, then you might want to borrow a cooling system pressure tester, install it, heat things up, and look for pulsations on the gauge when idling, all warmed up. That'll show up any significant combustion leakage.

The other source of added pressure when you rev it up is just the increase in pressure of several psi in the block and heads when the water pump revs up, and creates back pressure against the (intentional) outlet flow restriction of the t'stat. Your blow-out might just have been that simple.

BTW, Permatex #2 is more gooey and will not quickly dry up like a glue and seal like Permatex #1. #1 is more made for things like metal-to-metal sealing that is not meant to have any flexibility and is very permanent (unlike a gasket). (It is used, for example, in sealing together the 2 halves of the crankcase of small aircraft engines.)