I was fortunate enough to pick up one of these off a friend. It's a lovely piece that I've admired ever since it was released back in 1977... I will have been 15 at the time. It's probably a Norman Swales sculpt although I could be wrong... he still sculpts of course and Perry Miniatures have some wonderful pieces he's done. Looking at the kit I do wonder if the Minifigs Valley of the Four Winds Bell Tower was based on this piece... similar sort of make up. Could be wrong, siege tower illustrations abound of course.
The Tower, 25/BT, was priced at £8.20 and the cladding kit which came a little later I seem to recall, (25/BU) was priced at £2.45. Still need to find that one.
Love the fact that the logo was based on an artillery piece silhouette from the front.