i did that on my ke35 and used the holes allready in the pedal box to bolt in an ae86 master cyl and then welded a bracket on the pedal for the pushrod but it did not give enough of a push on the m/c and the car would creep foreward with the clutch pressed and in gear if you revved it, i moved the pivot point of the pedal higher and then lengthened the pedal to line up with the brake again
the idea of using the bottom hole in the pedal box as the top hole for the m/c sounds good but i had already butchered a hole in my repainted engine bay so i had to do it the hard way.