Welcome to C&V world, interesting project you are undertaking. I’ll offer a few things, most of the snags have been well addressed by the sages😉👍.
The stock Continental rear derailleur won’t handle a 39T cog, if one even existed. As said above, a Suntour VGT or similar long cage model would be the most widely available item. I think the idea of a mountain bike unit would be most likely to produce a working setup. A Huret long cage, (or the Schwinn Approved version,) is a possibility with about a 34T limit.
A Schwinn Super Sport freewheel, with the 32T big cog, that came stock would be about as close as you’d come. Again, an early mountain bike freewheel could give you more choices. I have the Schwinn Super Sport stock 32T freewheel for a restotation build, check eBay, and the For Sale sub forum, at the top of this forum page.
Best wishes on gathering the parts you need. Others here will offer up more knowledge and ideas, lots of good folks in this forum.
Bill
Last edited by qcpmsame; 01-03-22 at 03:06 PM.