Cool bikes and interesting examples regarding skip tooth termination. I would bet the drive train is original as everything else appears to be OG or age appropriate. There were plenty of parts available for either type drive train back then, so why bother? It would have been an expensive conversion with little to gain.I have two 52 Girls bikes with the serial # on the bottom bracket. The 24 inch New World has 1 inch skip tooth while the 2 inch balloon tire has half inch pitch chain, both serial numbers second half of 1952. Of course the half inch pitch may have had the cogs and chain replaced at some point.
I had considered that, although the bike is metallic paint. The serial number does match 1952 and 1957 bothIs the bike a middleweight? If not, it may be a 52-53 since some of the serials were used all three years. Never have I seen an original unmolested 1957 Schwinn with 1" pitch.