Ron,
You got me thinking... (I know... dangerous) so I came up with this idea... this is not to scale or anything, just an idea and it might suck for all I know. The idea is to:
1. Keep slot in floor to absolute min.
2. Be able to use any after market pedal...
So the concept is the "break pedal arm" (shown at bottom of drawing) is what comes through the floor. Slot only has to accommodate the width and travel of the break pedal arm. The bracket would be installed after the floor in in the car by bolting it with two or three bolts (shown with 3 bolt holes). The bracket is bent 90 degrees to provide a tab that any aftermarket brake pedal could be attached to... like a lokar for example... Just food for thought...