Hey-ya Wayne, et al, I had to purchase a 26.2 about a year ago, but I can't remember what it was for :( I know that there are at least a couple of frames that require this size, and I'm sure that others on the list will have the info. As for the allen bolt. My 27.2 SupRec post on my 84 Torpado Superlight has the same thing. It was suggested to me that the part was probably a replacement for the broken original. I prefer the allen head to a standard bolt, by far, and decided to keep it that way, regardless of "period correctness" or not. As it happens, I have the same situation with the cable securing bolt on that bike's Campy SupRec brake calipers. Again, whether original or not, they are soooo much easier to use, and look better to my eye, so I kept them too. Pictures available upon request...
Best regards,
Mark Agree
Detroit MI USA