Problem Solved!
The replacement Sea Stairs were here at Lamb's Marina in Jacksonville and the marina installed the new brackets to fit the stairs to the boat. As usual, the brackets had been slightly "improved" since our Sea Stairs were made and they didn't quite fit the old brackets. My old cover won't quite fit the new stairs either. However, the new stairs themselves are as good as the old ones.

Jacksonville insurance adjuster says she thinks everything will be paid with no extra hassle and that I don't have to lug around the broken sea stairs until some insurance adjuster can see them. She said the pictures and police report were good enough. I'll believe it when I get the check!