finding older bikes that take 32c is easy. In fact here is a long thread on that
https://www.bikeforums.net/classic-v...g-bicycle.html
But by and large most vintage bikes will be north of 20 lbs once you build it up. That's an aggressive weight for an older bike that you are not likely to hit if the bike is made of Reynolds 531, columbus SL/SP, or any of the good Japanese chrome moly tubing sets (Ishiwata, Tange).
Super vitus 980 built up a nice light bike and you could try your hand at a 650b conversion but finding an appropriate frame for a 650b conversion is another story.