Hi Phil.
My TROWA set (near 1959 - 1961) has all the drums in inches and all heads were calf in original -- I still store them carefully (with regular glycerine tissue wiping) and BD-heads still original fitted.
CONRAD heads were selled in ordinary musical shops and in the big special shop "Leipzig" in Moscow which was specialized for german goods in 70 - 80's. Musical goods were exported around the world by united DDR company (placed in Berlin) called "Demusa". Not so long I've seen an adv about selling low budget line TACTON set with cellulose shells in Britain -- its heads still were partly CONRAD.
George.