Phet, c'mon man, you know you can hit me up directly for help.

First, see my sketchup model. That will show you with pretty accurate measurements what should be underneath - at least what is underneath on the front half of the step.
The step is covered with that corrugated rubber flooring that you can get at Home Depot or Lowes in the flooring dept (I just picked some up 2 days ago). I think it was also used on the Pole Position cockpit too (based on seeing it in a red baron cockpit which is very similar).
I am in the process of moving my games back into the newly carpeted game room. I will try to remember to lay the SW down and get a shot of the underside for you. Feel free to bug me if I forget! And if you aren't quite sure what I'm talking about with the corrugated flooring, let me know and I'll also take a picture of that.