I have NOS Mugen engine parts for 1976-1978 CR125M for sale.
The kit comprised the following 1979 (#444) CR125RZ parts (which aren't hard to find NOS or used):
Reed valve assembly.
Exhaust manifold is stock (#400) 76-78 CR125M part.
I have the following key components for the kit:
NOS cylinder head
NOS 32mm Keihin carb
NOS Heavy duty clutch springs