From what I've read, the first Cycle Truck (Schwinn) came out in 1939, and the serial numbers began with "A" and went in succession, so "B" might be around that time frame. They started the numbers with "A" again in 1946, and again went in succession, so my guess is it's either 39/40, or 46/47. The cranks may have a 2 digit date stamp.
