Wow Admiral, that's the same ladder I just installed after I rebuilt my swim platform. Much cleaner look and more room on the platform!
Except we're getting older, so I used the four step. Easier to step into when your in deeper water. I also love the spring loaded lock, so you don't have to use a Velcro strap.
I will say , I got mine on Amozon for $79. But it must have been a fluke, because I just cked, and the four step isn't available right now.
Oh, and a ladder down alarm is a great idea ! I left mine down twice this summer, on a 7mile hike back from our favorite beach. I'm an automotive electrician, so it probably won't be hard to figure out!
So, Sam,. Hope our experience with these, helps you figure out what to do.
Happy boating !!!