HipHip Hooray! You got it!
I didn't even have one of them fancy air chisels. Gee you take all the work out of it!
The floor is hiding another of those secrets...
There's a lip along the north edge that's under
the plywood. Since I was one of those wimps who did not replace their whole floor, my way was to use a wood chisel and cut back the floor about an inch toward the 'north', starting where the alum. floor met the wood. The lip may extend around the side underneath, but I just don't remember about that. If so, you would need to trim that wood back as well.
Once that's done, some screws will be revealed which can be removed and the whole pan lifts out, if I remember right.
Hope that makes sense and let us know how it goes!