When I played it to some friends who are big psych-folk heads, they really liked it but were not entirely convinced about the date - this was especially because of the synth-y stuff happening. How clear are you about the provenance of the tape? Do you know the person it came from well enough to be sure it was a genuine 1970s radio recording rather than something mocked up to sound like one?

One of the suggestions, if it is a later recording mocked up to sound older, is that it might be something to do with the mysterious Robyn Nice, the anonymous Chicago based loner folk artist who,since the late 90s, has released multiple recordings under a series of pseudonyms, with them often coming to light via unconventional routes.

More here:About Robyn Nice

And a Bandcamp page collecting some of his releases:Robyn Nice archive