[Audioarchivist]

Yeah, print through like you're describing in an old-time radio show (I'm assuming it's talking mostly, not music) is pretty hard to get rid of - like C.S.I. forensically hard to do!
The only thing I can think of is a noise reduction filter that lets you sample "what the noise is" and then apply that to the spaces between words only. It would take probably thousands of small selections done manually, each time re-sampling "the noise" and applying it to the silences... For example:

If the tape said:
"The quick brown fox jumps over the lazy dog"
but you can hear:
"The quick brown foThe quick brown fox jumps over the lazy dog.ver the lazy dog"
You would select the first half of the sentence in the noise filter as your noise "profile" and apply it to the pre-print through. Then select the last half of the sentence as noise and apply it to the post-print through. Lots and lots of manual selection labor and countless small patches later, you might clean up a little of the print-through...
I'm just theorizing with this suggestion, and it would be a helluva lotta work! It might not work so well, either, depending on if you can find a noise reducer that lets you make a "noise profile" to tell it exactly what noise you want to remove, and it will probably sound very "artifact-y"...
I think Leif12345 has the right idea - just leave it and "suck it up" in your mind! There's probably not much that can be done to fix it without very long hours of labor...
Sorry to break it to you like this!
Good luck, and if it's totally worth doing and my idea works, let me know!
Cheers!