Thanks Dutch, but my old school reckoning leads me to believe that 15/64 is actually 1/64 smaller than 1/4, or 16/64. (divide each side by 16 and I get 1/4. so forgive my reluctance to buy them.
I did however call Stateside who say they have not sold any BSA rollers in the last 10 years. So I time warped right outa there.
Having Dutch inlaws, and other rellies, I have shown some diffidence in making contact with Holland. (I have yet to be right about what day of the week it is, and that very question can cause the outbreak of a Royal Commission)
so i had a crack at the Poms... and lo and behold the order is filled both 1 & 2 thou oversized rollers are on their way. (Here's praying the packaging is good and they don't get mixed on the journey out to the antipodes.)
Thanks for the help and clues. the new bike will be one step closer come Christmas.