Well here is what I have to explain the recess booster mod. We use an 8" dual chamber booster and years ago I bought like 10ft of Material from the steel yard that give a nice .25" gap all around the booster. Then we cut it to length or the depth we want to or can recess. usually to the first fold in the booster. Then I laser cut a pile of plates that bolt to the booster. I take one of those plates a weld it to the ring, then I cut the hole in the firewall and mock up the whole booster and master bolted to the ring to get level. We than tack it in place for level and the SLOWLY weld it in place. It will warp a firewall way to fast if you not careful due to the thickness of the steel the ring is made from.
You can see the booster ring to left under that dash. This pic was taken to show the LS1 engine ECU brackets we sell, but will give you another persepctive.
We then use the Kugel Komponents brake pedal assembly. It gives a better ratio then most stock pedals not intended for booster and gives you a place to attach other things under then dash if you like.
Hopefully this helps. If your going to run a booster this seems to have worked well for us.