... the Boogie Man's Cache Mystery Cache

This cache is not at the specified co ordinates. You'll have to solve the first part of the puzzle to find it. And when you get there you'll find its locked. You'll need to solve the second part of the puzzle to get it open. You probably could force the thing open. Once. But that would break it.

There is a geocache nearby. Its exact location was once broadcast in a doubly encrypted messsage on a late night Kent radio show in the late 1980s and early 1990s

It shouldn't take you too much brainwork to figure out the location from that message. It might look as though the cache is on private land. It is, but it's there with the full knowledge and consent of the landowner. Mind you when you get there you'll find the cache is locked. You'll need to solve the second part of the puzzle to get the combination required to open it

If you are the sort of person who doesn't mind cheating you might be able to force the thing open. Please don't. You'd be more likely to break it than get it open.