Hi John,
Mny thnks pics of yr two late period No 36's. I have never seen any dated later than 1972, and I suspect that production run was the last. I have seen several in the poly bags, so probably a bunch got sold off as scrap, or whatever, none seem to have had a filling plug fitted.
As to finish, JSP 316, amended to 29/1/88, shows the body colour as "phosphated and varnished" and a golden yellow wide band. so yr eg looks to be right. No mention of red paint on plug, but this may be a sealing device or whatever to ensure waterproofing. Mine, incidentally, has traces of luting around the threads of the base plate, but, again, this may be pres rather than true waterproofing.
Unfortunately, much of this has to be conjecture, lacking, positive proof or documentary evidence.
Alan1