Here's some info as requested:
The new remo head is loose when sitting on the shell. I there is a gap about the thickness of my finger between the edge of the shell and the headring on the head.
I measured the inside of the tension hoop, where the headring would fit into it, and that diameter is 31.5cm so that is 12.4"
The old head has a headring outer diam of 12.4" and an inner diam of 11 7/8" (which is the size that remo says for their 12" metric).
The new Remo head that doesn't fit has an outer diam of 12.5" and a 12"in inner diameter
So, that is where the misfit is. The new modern remo head is .1" (.25 cm) wider than the head I removed and the inside of the rim.
I'll check with Remo and maybe a local shop.
Thanks