The easiest ways to tell a 1973 P13-9 from a P10-9 frame are the way the rear brake cable is routed on the frame's top tube (the P13-9 uses three chrome plated Campy cable clips, while the P10-9 uses two top tube braze-ons), and the P13 doesn't have front fork and rear dropout eyelets for fenders/racks while the P10-9 does.