Heres a sneak peak, if this gives you any ideas for mounting the pedal box.
 
Due to the curve of the firewall, if you raise the pedal assy up about 50mm you can go forward about 50mm without cutting the firewall, but by raising it up that much means you will clear the lower part of the firewall double skin section, and once you cut a hole, theres a nice cavity from factory just waiting for your master cylinders to go in.
 
Looking at the pic, the greenish primer panels in the cutout on the back, right side and bottom are there factory, i have not added those, the left side which you cant see in this pic is just a void, no side wall thereuntill i guess closer to the fuel tank tunnel.
 
Also the AP Racing CP2623 extra short master cylinders are the way to go, they are very short and have the outlet on the top, not at the end like most, which that alone will make it shorter.
 

Reverse floor mount or hung? 
 

Thanks for adding the mods you have made. It looks far more refined than my backyard job. Mine has the 3" cylinders but they are still too long for where they are fitted but the top point fitting would make all the difference. Have you made sure you have enough clearance to operate the top of the pedal? With the tilton unit, you do need to use the top of the pedal to manage enough foot pressure for braking. The steering column is very close to the pedal assembly so, if you have a big foot it may clash the column. The co-driver in the 300 had this problem with my car. Just something to think about when fitting the column nad setting the height of the pedal box.
Trav, you should look at having a structual box fitted between the chassis rail and tunnel, 30mm below the floor height so you can set the pedal assembly with a far reduced chance of fouling on the steering column. It would also help with access around the a car with roll cage.
 
This car will be fitted with top hung pedals.
Ian has provided a set of cusco coilovers and a oil cooler for $50 which need new shocks but still very generous gesture.
Just need a set of rear hubs and the car will be on its wheels and ready to be sent to the roll cage fabricator.
 
 
 

Any progress on this build?