If the tapes are truely 70's the ATT tapes may be interesting if they have some of their technical operations documented. ATT was the long-lines of all three networks in the day. On Friday afternoons after the networks went dark after the soaps for the afternoon, ATT would feed a BW program explaining all the weekend NFL timings and patchings for Sunday games.
It was a treat to watch. A bunch of guys in white shirts and ties with shirt-pocket pencil protectors in place explaining every hard-patch from stadium to NY, all the patch points along the way, all the times that a second game should be patched to NY, and all the patches from NY to the regions that would get any game. It went for 20-30 minutes on our feed at my CBS affilliate.
This ATT video from 1967 shows a bit of the ATT video at 13:00 in. (And some looks at early color from the day). And then more on voice/teletype services. This is how it used to be.
http://www.youtube.com/watch?v=ZAJpionUxJ8