looking at the 360 heads in the shed that taper is there and the autolight 65 plug has the washers to seal it.

I have never saw a stock SB head use a taper plug.

now my 452 440 heeads use the small peanut plug with a taperd seat.

I have saw a lot of them have oil at the plug and in the threds but has always been from from other oil leaks,windage, yrs of no cleaning.

dont overthink it.

if you think they are leaking,mix some dish soap with water and fill the gap around the plug,run engine and look for bubbles.

chase the oil leak with baby powder. same on a trans leaks.