Originally Posted by Hobbiano

You might want to consider something like a mid-nineties Trek 520. I've found a couple over the last few years - a '95 and a '96. One cost me $250 and the other $180. Both on local craigslist.
Both have lots of clearance for larger tires, 37mm - 40mm, and oversize True Temper steel tig welded made in USA frames with 135mm rear dropout spacing. Decent Shimano components, 7-speed, but easily up graded to 9-speed.
Not exactly vintage but only just modern enough to be easy to up grade or find parts for. And a well thought of tourer.
There is lots of info on these in the touring sub-forum and catalogs with specifications on the vintage Trek site.