Terry, I understand your problem is that the OEM sway bar hits your new calipers. This has little to do with a firewall bracket, to mount your booster.
Something is terribly wrong with your setup. I use Scarebird spindle brackets to hold my S-10 calipers. Most of our members do as well. These spindle brackets position the calipers on the BACK SIDE of the rotors, far away from the sway bar ends. We get full range of turning radius with no interference and no welding is necessary. The only ABS parts I know of that work properly is the combination booster/master with firewall bracket and pedal hardware (ABS #9787). NOT spindle components.
JohnG and I were just talking about different Squarebird brake setups a few hours ago. I know there are kits available that use 2-piston calipers (Wilwood) that don't fit the same way as the S-10 single-piston calipers. Wilwood makes fine racing products but OEMs predominately use single-piston calipers and so do I because they are simple with fewer parts to go wrong. I have seen setups where the calipers are mounted on the front side of the rotors. This does interfere with the sway bars, so stay away from any setup with calipers mounted in the front.
I have heard of setups that completely abandon the sway bar (this is not good). My suggestion is, buy a beefier 1-1/8" diameter sway bar. I got mine from Lance Herrington at Thunderbirdsouthwest
. I also suggest using Scarebird spindle brackets that are designed for your Squarebird OR 1959 Full Size Ford (Fairlane or Galaxie). It's the same part number. These brackets hold S-10 or S-15 calipers and pads that are available everywhere with a wide variety of pad compositions including ceramic and semi-metalic.
BTW, I heard nothing regarding a combination proportioning valve.- Dave