cylinder foundry markings

Hello

I was  cleaning/sorting my shelves and found   a  Norton cylinder dynamo type which looks like 500 cc.  It has 8 fins. I do not remember where I got it. I have  several heavy twins but cannot remember such a cylinder.  See my Model 7 from my father in picture above, and now  myself ageing. Although I learnt with it, I always look for memory and knowledge.
The cylinder has  a threaded  base  in front  for a dynamo.  I measured the bore and read 64,5 mm. Strange.I checked the size of Navigator barrels but there is no dynamo in front o
Books indicate that the 88 standard bore was 66 mm.
I checked the barrels and cylinder fining and saw no sign of being fitted with new  liners. The cast iron between the barrels and fins is seamless.
The only foundry marking is a big R on the inner lower side between barrels. It is not stamped but out of foundry clean.
So my question is: is it a piece which came out ot foundry and was never finalised. And got out with  parts of Norton  going out of business?
For the cylinder bore, the best I can do is to bring it to the workshop and bored  to standard size with new pistons. What about the bore of the cylinder tunnels  for the cams followers? Did they need to be machined too?
Or should I keep it as a design object in my dining room?

Thanks

René