after bit more tinkering it looks like the opposite side has also a different cylinder??
so now thinking this good side with the MM cylinder may have been a bodge,and yet was the better side which i stripped down…
as you said charlie I’d have expected the brake parts to be off the shelf cheap as chip’s item’s from back when these were made,but what was around back when these were built?? not alot with 5 stud fitment and even the drum backing plate is an odd one – spend hours looking at images of parts from late 70’s – 80’s to see if i can find a match