There's a group on the CABE that lists the king size versions. Your frame is 2 inches larger (seat tube measurement) than all the other Schwinn cantilever frames. They were only made in the early 60's.
That chain wheel setup is something I've never seen. Is it a two speed? Schwinn doesn't show that on their advertisements or pricesheets.
For ID, your serial number, on the left rear dropout, will have a letter then numbers that will give you the day month and year it was made. The first number will be the year: 2 is 1962, 3 is 1963, etc for the bikes of that timeframe.