Follow up,
In the end I dressed/polished the starter gear hub with crocus cloth, because I had some handy.
I use the better of the 2 sprags in my possession. The difference in lobe surface was visually almost indistinguishable
to the naked eye, 'specially a 53 yr old one.
(Both sprags had been modded with the CR seal spring)
I put a solid charge on the battery and next morning the bike cranked over like a 2 stroke and operated as designed, for the most part.
Thanks for reading.