Well, it took a while but I'm back at it. After the wire wheel, a vinegar solution, I applied Gluvit 2 coats. Z Channel is back down with aluminum rivets and SS screws, there were already 2 holes from a previous restoration. Bought enough pink foam board to displace 700#, most of it is in the floor and I have plans to put some a few other places. My trusty side-kick in the pic is pondering the physics of the caulk gun and how it works. It's loaded with GE Silicone II for Metal & Aluminum.
The old floor was in good enough shape for templates. The new floor is 3/4 marine plywood that was primed all the way around then painted with 2 coats of Valspar Exterior Porch Paint. the final coat will be Valspar Anti-skid, that has sand in it and I will add texture chips. Securing the floor was a pain as I kept breaking off the #12 x 1-1/4 SS screw heads, that or they 'bit' the wood but wouldn't grab enough Z channel or rib to pull down all the way. I tried different sized pilot holes, drilling out a larger counter sink area with a 1/4 or 5/16" drill bit. It didn't have a rhyme or reason why but I have to clean up a few broken screws.
In the last pic I thought about shaping those cut out pieces to cover the rib holes. If I can drop screws down there if sure I'll drop sinkers, hooks and probably my car keys. All this and not one run away screw through the bottom of the boat, Success !