Gentlemen,namely L.A.B and Rudi.

Thank you for the replies and advise.
I have found a used rotor in my garage (probably been there for 20 year )better magnetism
and when fitted the alternator covers the rotor, with no alternator over lap.
I have yet to reassemble, start and test the machine, but it does look very encouraging.
Many thanks' for the rotor suggestion.
I am most grateful.
Yours Harry

I also must use this as a salutatory lesson in
garage organisation, I have so many bikes and spare parts bought over the last 45 odd years I find it difficult to keep track of spares etc.