I used 1-1/2" machine screws.
While you're at it:
Pull the floor section, remove the carpet (reusable) and draw a template of the section on a 3/4" piece of commercial grade plywood.
While you're at Lowes (or wherever) pick up a quart of 3M fiberglass resin (it comes with hardener). Coat the wood floor piece with the resin. It's now waterproof. No need for marine board.
Glue the carpet on just like it came off the original floor piece. I personally do not use screws for securing the floor but that's your choice. I filled the holes in the stringers with an epoxy filler and called it a day....no screw heads, no alignment when you take the floor out and put back in place... just much simpler all around.
For the hinges, go to the hardware store and use #10(or your choice) machine screws and accompanying T-nuts with four studs on each nut. I actually added a little glue to each nut before I installed, to glue the nut in place in case I hit an angle while pushing in a screw and did not want the accidentally punch out the T-nut.
You can figure the rest of the installation. I did this to my machine last winter. Works like a champ, secure hinges, and a sturdy lifetime floor. No more honeycomb aluminum for me and no more removing the floor and the engine cover in one connected piece.
Do it right... :D
A nice and easy Saturday afternoon project. The resin dries and hardens within an hour and ready for continued work.
Forget this other crap of backing plates and what-not..it's a temporary fix. Sturdy but temporary.... The honeycomb will eventually soften, sag, and crush, so fix it now while you have it out. I did the rear and front removable sections on my machine.
I'm fixing to do a 96 Prostar 205 in a few weeks. Same piece of plywood, same resin, etc... Your material will go a long way if you have friends with similar needs. I have also ordered new lift supports for the engine cover. That will stabilize the engine cover a lot. Found them on Amazon ( http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1