Shelby? similar to Lindy models?
The rear seat post cluster, hard to see, but looks pre-balloon Shelby-esque; some curves, fat bridge tubes.
The chain adjusters, look like they might have room between the threads and square head to place an o-ring, not sure how common those are.
Also, Shelby may have used a British Fine Thread, 1/4"-26tpi - too hard to count in pictures; Schwinn may have used 1/4"-24 UNS.
The support (is it a bolt-on) for fork truss rods looks like those seen on Shelby's - did Schwinn use supports forged to the crown?
I believe Shelby had ~2-5/8" head badge holes, and Schwinn ~2-3/16" but again too hard to see in pictures.
Looks like the chain is about 1" too long.
Chain ring pattern looks Sears Elgin, (sometimes sourced to Excelsior Michigan City). Look closely, it has a fairly standard drive pin, but has a tab of extra material to drill/punch a hole for a 2" off-center drive pin also; weird.