Thanks Jingle. I actually did see another of these machines, locally, but it had no manual.
I found one old JCPenney ad for a model that may have been this one in a 1975 Florida newspaper with blurred writing, but I would have to pay for an expanded subscription on the newspaper archive site to be able to read the ad (and that might lead nowhere, anyway). It seems my paid subscription never allows me access to the archived newspaper items I want to see. I found a similar machine in a 1970s JCPenney online catalog, but there was no information about the manufacturer of that machine.
Surely, someone somewhere has a manual for this machine. The fact that I found two of this model locally, and that it was sold by JCPenney likely in the mid-to-late 1970s ...likely sold all over the USA, tells me there should still be manuals for it.