I'm pretty sure Two boots = Dual Piston correct?
You seeing two two dust boots on one side. That's a four piston, fixed caliper.
kelsey hayes, chrysler version, probably the most common variation. (the early ones have some very minor differences which I don't recall)
do seem to recollect it taking quite a bit of leg to work the manual brakes so your comment on the 7/8" bore requiring less pedal effort certainly got my attention. I like the idea of less pedal effort but also wonder if the currently in use Geometry, Piston Rod? etc., would work if I changed over to just the 7/8" bore MC.
The smallest diameter master cylinder for that system had a 1" bore.
Otherwise they look very similar to the one you have.
All of those master cylinders are somewhat pricey these days. There weren't nearly as many as drum brakes to begin with. Then at some point the big remanufacturers like Cardone decided it was OK to remove the residual valve from the primary outlet of drum brake masters and sell them as replacements for disk brakes.
Though there's no shortage of parts stores around my area, the days of knowledgeable staff seem to be a thing of the past and all the college kids populating my local stores can do is look it up on the CPU. Hell, I had to go to four different stores last weekend just to get a 180 degree thermostat for the RB, one kid even asked me what's a 440?
Do you know what (Yr, Make, Model, Eng) I would be asking for at the local parts store if I were seeking this 7/8" bore MC?
I think you have a few choices, none of which will involve a parts store unless you know one with access to really old stock.
1. Use the 1 1/32 master. Rebuild it yourself if the bore is free of pits and deep scratches. Otherwise send it out.
2. Trade or sell the 1 1/32 master and get a 1" bore cast iron version.
3. If you want shiny, see if there is a 1" or 15/32 version from Stainless Steel Brakes. When I last looked they were selling there own version of the K-H 4 piston system.
4. If you want light weight, see if Cass (Dr Diff) has an aluminum and plastic master with 1 or 15/32 bore in stock.
Observations on Decision points.
On the fire wall, the photos show a power brake bracket and linkage from a kelsey-hays 4-piston system.
I had one, I think it originally was from a 70 or 71. IIRC the linkage slightly changed the pedal leverage. This dropped the position of the brake pedal to be closer to the accelerator pedal - a plus. But it also meant a shorter stroke, and if there is no booster, more pedal force would be needed.
What you have looks like a clever set up to provide clearance for those headers.
If you're keeping those headers, then your choices will be a different than if you're changing them.
One other thing you can change to reduce pedal effort is the brake linings. Work with someone knowledgable to select a lining that is a little grabbier under the conditions you'll be using the car. Make sure to do the rear brakes too. Having appropriate linings and having them adjusted make a big difference on the initial braking.
Some references about the 4 piston K-H calipers and hydraulics:
1967 Disk brake service guide
1972 Chrysler Disc Brake Service p 1, Master Technician's Service Conference (Session 293)
1970 Imperial & Chrysler Brake Hydraulics Facts Reference Book (Session 274)
