Thanks Jeff. I bought a new set of the SuperStock slicks (no grooves) in '69. I still have them. They're labelled 8.90/9.00 - 15 and the slick is actually 9.5" wide. They're XS-11s
Unless we've missed something, I guess that nails them down to '70-'71 because of the change in size labelling. Funny this is, they don't have the white in the M&H lettering. Mine from '69 do.
I'm still confused...
Verne