Your gonna have to make up some el brackets with hole in them to slide a round bar through them. Have the holes so they are four inches from the bend that bolts to the firewall. Make the bar long enough to go from the piston to where you want the pedal located. Mount the brackets to the firewall high enough so that you have room for the proper ratio (you can find that at MPBrakes website)between pedal lenght and to fulcrum.
Weld the pedal arm to the bar. Tack the lever arm to the bar in the approximat location and see hpow that works and adjust as necessary. Use a hiem link on the lever end to piston.
I have seen some very inventive linkages here and on the HAMB.
Trial and error. You may have to do this a couple times.