The pedal box is pretty easy to make to a different size and shape I have done that for a couple of different models. If your floor sits on top of the 4" frame rails it can be accommodated by that. Shelby box is 3-1/2" to 5-1/2" high back to front and 6" wide.
The more time consuming parts are all the clevises, rods, pedals and internals.
Pedal Box Assembly, Clutch & Brake CSX Pedal Box Assembly, Clutch & Brake CSX [427 289 CSX CCX KMP ACE HT] - $725.00 : Acton Custom Enterprises, Custom Metal for Cobras