Tadd,
If you fit an RSR Style pedal box you will have to cut the floor of the car and weld in a new section as the RSR Box keeps the Master Cylinders outside the passenger compartment.
The SCRS box is better as it re-locates the cylinders inside the passenger area but it doesn't work with a standard pedal board.
We have seen several pedal boxes of this type fitted without a board and this does create some risk as the accelerator pedal stop is a part of this board.
If you remove the board then there isn't a feature to limit the accelerator pedal travel other than the carb linkages.
In the limit the side of the pedal box, which is only around 1mm thick, can deform and the rod from the pedal to the reverse link will misplace and potentially jam on the centre tunnel and life can become quite exciting.
We have made Bias Adjustable Pedal Boxes for years and the brake pedal has been designed to work with a virtually standard pedal board - the slot does need to be slightly widened.
We also use a bias bar with 'overtravel' protection so that if one circuit fails the mechanism doesn't jam which is a common failure with bias bars that used a spherical plane bearing.