Yup; my 1979 Raleigh-made for Intersport "Grand Prix" takes 700x38c tires (Bontrager Satellite Elite Hardcase) comfortably, with room for fenders front-and-rear. Of course, I'd never turn it into an SS/FG, but sounds like the OP should get a free/affordable "made-for" frame built from high-tensile steel "pipe", rather than searching for one 'o them thoroughbreds made outta double-butted 531.