X Head Assembly & Installation - Comments Requested

Do you know how many times the head bolts have been reused, retorqued ? They do fatigue. New head bolts might be a wise investment.
All too often what was thought to be a head gasket water leak turns out to be a intake gasket failure ( although you didn't say water leak ).
Minor head milling effects intake gasket fitment and we don't know how much milling has been done to antique heads. Aftermarket aluminum intakes may add to the misfit, possible gasket failure. So... Pay just as much attention to the intake gasket choice and fitment, as the head gaskets. Good luck with it.