^^^^^^^ This. Then throw in the already-mentioned variations in BB shell clearance and top-tube angle, and the real sizing answer is -- "Test ride it". Well, you can eliminate extreme outliers based on standover height, if you can get the seller to measure it for you before you venture out.

As for selection, along with the above-mentioned Schwinn "Cross" series (esp. CrossCut) and Trek 7-series (esp 730/750), I would throw in Specialized Crossroads and the various Univega models of the era as good candidates.