I'm the Wiz, and nobody beats me!
I've never seen an online 1951 Catalog. I usually don't give any merit to the chain pitch shown on the girls bikes during the 50's. Schwinn was slowly getting out of using the 1" pitch drive trains at a slow pace until they were no longer used sometime in 1954 and completely gone for the 55 model year. Stamping out a 1" pitch clover ring along the same time they were stamping out the 1/2" pitch clover probably seemed like a wasted effort at some point during these years.Also, the 1951 Catalog shows a skiptooth crank, which apparently was changed out as production was going on.