Neil, We always referred to the wheels as 27's, now known as 700 c.
Most had 27 x 1 1/4 for winter, wired on, which were 27 inches diameter less 2 1/2 inches to the wire bead. Mine were always tubulars, so the overall diameter was less, generally down to 26 1/2 inches, but always referred to as 27's. There were previously 26 inch tubulars.
Most people in 1960 had frame clearance for 27 x 1 1/4 and mudguards, which meant long reach brakes with the best wheels in. Some had frames specified with close clearance.
Keith