Hi there, Brian!

In fact, with the 7*7 matrix, and using a blahblah-handed blahblah, it was possible to solve the code. Although I doubt that was the method of the original encoding, it is nevertheless a consequence of that method having been used.

The plaintext is, of course, also admirably suited to the puzzle itself.

I haven't set out the solution as I felt this was an attractive problem that others should have the chance to puzzle out for themselves.