Thanks for all the replies,
Its basically the whole alternator set I want to replace - stator, spacer and rotor.
I'm only going by the CMS micro-fiche which has the same alternator shown for all years 73 -76 (CR250M and CR250M1)
My current alternator is points and condensor - no CDI and it has the usual coil mounted on frame under the tank
The NOS version on Ebay is advertised as having part number ending in 003 not 811 but they claim its for a 76 model which is what's confusing me.
Having said that, the one on Ebay it looks exactly the same so it would probably be worth the punt to buy (I think)