I have a 336 myself and had the same dilemma. I was told by a knowledgeable fellow that early 36 chiefs had the screw in caps. Conversation with a well known AMCA judge, however yielded a firm "no. 36 chief was bayonet only. Four cyls still had screw ins in 36" From my own research however, and I could be mistaken, I believe that 36 was the first and only year of the left hand case breather tapping just forward and below the front jug which some people claim was for a timing mark view hole.
At any rate, the tanks that came with my bike have 5 tappings in the bottom of the oil tank. They would be; supply, return, vent, drain, and..? gee! the additional 1 year only crankcase vent from the left side of the motor!
I don't know what production number they ran out of screw bungs at, but I believe that as long as those tanks have the fifth fitting, then I'd argue it till I was blue in the face. And I have!
AMCA Yankee Chapter
36 Mag Chief
48 Mag Chief
A bad day spent fartin' around with motorcycles
beats a good day doin' just about anything else.