Slant 6 blown head gasket causing low compression?

Judging from your pics,,,,I think the head was not hardly torqued completely down .
Looking at the head,,,,you still have good witness marks from the fire rings .
The gasket was clearly leaking,,,,,but I think it was caught before major damage .

Your exhaust valves still show good color,,,,,a nice tan which means they are still sealing well
and not burned .

I would clean the deck very thoroughly,,,,,,and inspect all the bores and piston crowns .
I would have the head surfaced flat,,,,and a nice valve job,,,nothing major,,,,,just smooth all the seats again .
Valve stem seals,,,and a new gasket set l

Unless,,,you are wanting to rebuild anyway,,,,then go all out and make it new again .

Tommy