Ever seen one of these?

well if you really want old, there use to be a gizmo so you could use your 4 track tapes in your 8 track player. the 4 tracks did not have a built in idler

i think they used to make FM radios that would plug into the 8 track

Yep, 8 track and cassete both had an FM radio adapter.

Remember the old FM signal amps?
We still use those, because they still work great today. :D
You can pull a good FM station from 100's of miles away, and my Brother uses one on his Honda Interstate because thier anntena's are not all that good for the stock sound system.