I haven't started the install yet, and I'm still waiting for Triton to respond with instructions. I guess there's less motivation since I paid already...
Anyway, I'm guessing you'd use 2 bolts near the top, with the nuts and washers inside the splash well. I've heard the lower screws are more like lag bolts that just go in to the core, but I'd personally rather take the tank out and go through so I can undercut the hole and use epoxy.
I'm not sure you even need the lower fasteners if you were using 4200 as a backup since the top ones are the important ones when putting weight on the step. But it might be possible to just do 3 bolts through in a V layout (2 at the top corners, one lower in the middle) with the lower one just high enough that the hole is in the splash well.
The reason I haven't made progress installing mine is partly due to the weather, and also partly because I haven't decided how to repair the old kicker bracket holes where the swim step is going. Gelcoat patch kit? Life caulk? Bare epoxy? Take it to Tern Boat Salvage for a professional repair?