Can you see marks on the frame where a tank rubbed? It might not have had a tank. With tank, model B607, without tank, model B507. The B507 usually didn't have a rack either. The rims look like S2's and the truss rods are the thinner 3/8" size so that puts it somewhere around 1950. What's the serial number? They don't get much better than that for $150. 8) Gary