Bill what a great idea for a project! No way on Earth I would've thought of it!
I'm curious about the 'cast iron' bit. The tower was built of cast iron sections or panels? That seems very strange.
Fightin' Joe.... I too have always been fascinated by the disappearing guns and other coastal artillery. An articulated model would be tough, but fun! Do they make a kit?
Also: Have you ever researched the Fort Drum that was situated in the water near the mouth of Manila Bay? I believe it was a steel and concrete structure built upon some protruding rocks. It was in the shape of an old battleship's foredeck (I can't spell foc'sal except for forecastle) It featured two large caliber double(?) or triple(?) gun turrets.
My ship (USS Fresno LST-1182) passed it twice in 1974.....both times I was on duty in the engine room. The only pic I ever saw was pre-war. I'm going to look it up, but wondered if any here had heard of it.