I think you'll wind up with something very different than your Serotta. With 600 arabesque components, I'd shoot for a frame of the late 70's or early 80's vintage. Once it's built up it will be a bike to take on longer relaxing rides. Set it up with accessories different than your vintage cross bike (with something like a larger roll seat bag to carry a jacket along on fall rides) and it will have a place of it's own. 650b might be another option if you find something like an 82-83 trek that are sort of low trail already.