I used the entire kit sold by CPP. First, the under dash pedal bracket assembly
needs to go in. THis means the existing stamped sheet metal column bracket gets cut out.
The new pedal/booster mount assembly goes in with the 4 booster mounting bolts
going thru the firewall. You just tell them you are doing front discs and rear drums and they include the proportioning valve and is pre-mounted on
the booster/master cylinder. No clearance issues; I stuck a 455 Buick in mine
and no issues. I have front discs & My rear end is a 56 Olds. I have great brakes and the pedal assembly is VERY stout. The only clearance issue inside was where the bracket bolts to the bottom of the column area. IN my case my new AutoMeter gauges were just a bit too close to the bracket; so I had to grind a small amount of material to allow for the fasteners on the gauges..... So, if you are going aftermarket gauges
just trial fit before bolting everything in. Like I said, I needed to free up room underneath for exhaust/trans/trans cooler, etc.
Hope this helps.