Hi.
yeah, 80's from the looks of it. Find out the size of the rear hub. During part of the 80's Cannondale
used a very hard to find hub. I think it was 122mm, but don't quote me on it. I had one of them, and replacing the rear wheel was a nightmare because nobody has that size any more..
I also suggest getting the largest tire you can fins that will fit. One good choice
would be the Vredstein Fortezza 25c.