Re: 1948 Whizzer Pacemaker frame number.
Petcock appears to be original. The 705 Carter was used on a REO lawn mower motor, not Whizzer.
#724 is a low serial number and was most likely made by Whizzer, not Schwinn. Rumors have the first frames made by Cleveland Welding [Roadmaster], however some claim Whizzer made the first frames. Schwinn took Whizzer to court and the settlement was to have Schwinn make the Pacemaker frames for Whizzer.