Amazing find, well saved. It is shocking what people are prepared to dump.The Zonal tape is robust and in my experience does not suffer from the sticky shed syndrome.
I have a few radio station tapes, which I have picked up second hand over the years or been given, they generally fall into two categories: a) edited 'productions' or 'spots' ready to be broadcast; or b) raw speech recordings such as interviews (which are/were to be edited). If the former then there is usually little tape on the spool, just sufficient for the duration of the feature in question.
At the moment I am digitizing some 1961 ATV and BBC Panorama, Tonight and Searchlight TV recordings I came across whilst looking for material for my Found Tapes
Archive. Real time capsules taped off 405 line TV. So do check the contents before erasure, might be something interesting there!