I had originally purchased Mustang Steve's template and pin for the brake pedal, intending to use his complete setup. Then, I found out where one of those two inches that we hear about in Mustang engine compartments is. It's between the center line of the compartment and the master cylinder centerline. Steve's recommended booster wanted to be inside my left valve cover.
I decided to do the Geo Metro master cylinder conversion, but could not find rebuilt parts, so I searched for a similar booster that WAS in stock at my local CarQuest. That turned out to be a late '80s Nissan Sentra booster. I used Steve's template because it already had the holes in it for the pedal support and the firewall. I then transfered the boosters hole pattern to the template, bolted the template to the firewall and drilled the new holes. Then I followed Steve's instructions for modifying the pedal support. The hard part was opening up the firewall end of the pedal support to clear the rubber boot on the booster. The hole in the firewall for the original master cylinder must also be opened up. I found that the hole in Steve's template was the same size as a 2" conduit punch, which I just happened to have. Then, I put some silicone in the extra holes in the firewall, and around the stud holes of the booster, and around the rubber boot to seal the firewall. Then I bolted the booster up to the pedal support using just the four 8mm studs from the booster. The operator rod from the booster is a 10mm stud. Steve makes good arguments for changing the pedal ratio, and I decided to do that rather than hook up the rod directly to the pedal. I've heard that the Geo setup is rather "touchy", and it is some what easy to change the ratio. The '63 brake pedal has a through bolt for connecting the M/C rod to the pedal, so I just drilled an identical hole 1-1/4 inch lower on the pedal, then designed an adapter to connect the operator rod to the pedal. My son is making that part out of 6061 aluminum.
The Mustang SVO master cylinder that Steve recommends is about 1/8 inch too long to fit between the booster and the spring tower, and the there is huge interference with the export brace. Back to CarQuest, and I found the late '90s Subaru Legacy M/C that fits right on the booster. It is aluminum, has a 1" bore (I've got 4 wheel discs), and comes with a fluid level sensor in the jar. AND it fits perfectly.
One of my deciding factors for the Subaru Legacy M/C was neat bottle with a fluid level sensor in it that I have connected to the parking brake light.