KABAR2, Sounds like you know a lot more about this island arsenal than I do. The only thing I can add was that a Kingston City cop and I rowed over there in a little 10' rowboat in 1972 and we started below the island so the Hudson River current was quite a challenge to overcome. We finally got there and looked and looked, but only found a few Buffington rear sights for the Trapdoor Springfield rifles, all rusty, of course. It was interesting, but you really have to watch your step there. Surrounded by water as you are, snakes are common. We used to go out and hunt rattlesnakes and copperheads for my friend's uncle who milked them for a local university.
Also, as the story goes, the late Val Forgett, as he was leaving the island all loaded down with munitions, spotted two enormous 14" Naval Gun shells from WWI flanking the end of the pier, so he turned around and went back to tip both of them over and into the Hudson River mud, probably about 20 feet deep there in the lee of the current.
FYI,
Tracy and Mike