Here is an update from the Schwinn forum (not sure who the quote is attributed too though ...)
----------------- I know this bike well. There is no serial number. It is a one of a kind as far as I know. It was raced by Jack Simes and Jack Heid [III?] in 1951 to a 3 mile tandem race championship. 6 minutes 1 and 2/5ths sec. The race was in Johnson Park, New Brunswick, NJ. It has been changed quite a bit .. Thought you'd love this attachment I have another one similar to this one but was used in Helsinki in 52 by Disney and Heid. -----------------
http://www.schwinnbike.com/
Bob Hufford
Springfield, MO