HI
Without wishing to "teach granny to suck eggs". Are you absolutely sure the head, or even the block (unlikely, But?) are perfectly flat?. Also, re the leakage, have you considered checking the head, particularly, with NDT, micro cracking is hard to detect visually, but should show under dye penetrant.
Reading what has been written, I don`t think improper Torquing is necessarily the issue. Though the state of the Head gasket would suggest a lack of such?. Which would beg the question, is the torque wrench accurate?. "Back in the day" our`s where re-calibrated on a frequent basis. Another question which niggles, Do the flanged washers need a different torque figure?. Using separate washers, there are two "sliding friction faces" the flanged washer has only one.
Generally speaking, the manufacturers tolerances where usually "sufficient" for purpose, so increasing the torque, as some would, to get a tight joint, would be more likely to over-stress the studs/bolts.
I note also, the use of an NOS Stanpart Gasket. Copper, age hardens so could that be contributory?
Pete