I could not find any threads on this topic that had any more detail than just a brief paragraph, so I figure I'd pit my experience out there.
I started by determining how much to widen the old master cylinder hole on the firewall, I opened it to about 2 1/8 inch, instead of grinding with a die grinder or carbide bit, I got a Milwuakee hole saw. I took some 1/8 inch flat bar, and made a bracket so I could center the hole saw and hold it steady when drilling.
From there I made a template out of scrap wood, transferred the markings onto the firewall and drilled accordingly.
You can see as well I had to modify the column bracket, I took one of my extras and chopped it up to clock the other bolt hole in a new location, keeping a factory style appearance, and maintaining rigidity for the column.
Going inside the cab, I had to remove a lot of the bracing in this area for the booster mounting holes/flange. I want the firewall to be as strong as before, so I took some of that 1/8 flat bar and welded it into the old brace location, and as you can see I seam sealed and painted it.
Now it is fully flush mounted. The only thing I do not have in here is to drill the old brake pedal assembly bracket, but thats a given. I will more than likely take the old studs to the bracket pedal bracket and reverse them to fill those holes. To accomplish this I may have someone machine me a 1/8 plate to sandwich between booster and firewall, much like the hydroboost setups do.
Once I get to the pushrod setup, I will report back.
