Hi there and Happy New Year.
I am a mild expert regarding this very swap so I hope I can help you. However, please remember that I am NOT a licensed expert, just a backyard guy who has had some experience and learned from the experience of many others. There may be errors or omissions in my information. Therefore, if you have questions or concerns, consult a qualified mechanic.
The swap I'm talking about is the
SINGLE BEST UPGRADE you can do to your car. The information below will result in a well balanced and reliable braking system that is serviceable with parts available from any supplier like Rock Auto or the like.
Your concern about piecemealing parts together... all of the parts for this swap are available new or rebuilt from the parts store, with the exception of the actual spindle assembly. For that you need to find a 69-72 disc brake donor C body, or a 73 disc brake donor C body. Why the disctinction? The 73 Spindles only fit the 73 rotors. However, the 73 rotor is used in various applications right up into the 80s and are way more available and have some minor improvements, so if you can find a set of 73 spindles, that's the best option. I'm using 69-72 gear, and it works fabulously on both my 66 Town and Country wagon and my 66 Monaco.
Regarding kits - yes, there are kits out there from various manufacturers like Scarebird and Stainless Steel Brake Company etc. Most, from all reports, seem to work well. Some use proprietary (their own designed) parts like spindle adaptors etc, mainly to allow the use of commonly available Bowtie parts. Search around and look at reviews.
One point against them in my opinion is that none of them seem to address the issue if the power booster if yours is a power brake car. They all seem to say you can keep your existing drum brake booster.
WRONG. DANGEROUS.
The drum booster does not have enough power to fully energize the disc system in the event of a panic stop. Yes it will bolt up and work fine for 95% of your braking needs, but if that dumb kid on a bike cuts in front of you would you rather be able to have stopped before you ran them over or the 25 feet farther it takes with the wrong and weaker booster? My point is you don't want to find out the hard way.
So I always advise people doing this swap that you MUST use the correct Disc Brake booster when running a disc system swap.
The second point is I feel that many aftermarket systems use parts designed to work on lighter cars, and bearing spacers that leave me a little leery of their true ruggedness. Again, you don't want to find out the hard way.
Now - here's what I feel is the best option: Ma Mopar engineered a dandy disc system for our C bodies from 69 up to 73 that you can take advantage of...
All C body cars with disc brake systems from 69 to 73 use the same lower ball joint as the 65-68 C body cars with drum brakes. A big advantage, because all the disc brake hardware (spindles, calipers, backing plates etc) from the 69 and up cars BOLT RIGHT IN.
A DIRECT SWAP.
I am copying and pasting a bunch of documents on the swap - parts interchanging, donor lists, and what you need and how to do it.
There are a few caveats - if your car has column shift for example, there are a few C body boosters that may interfere with the column shift linkage. Cars with factory Autopilot will have fitment issues with the master cylinder...
Read on:
DISC BRAKE CONVERSION INFO FOR 65-68 C-BODY
FOR NON AUTOPILOT EQUIPPED CARS, ONE CAN USE
ANY 69-73 C-BODY DUAL RES DISC BRAKE MASTER CYLINDER.
FOR AUTOPILOT EQUIPPED CARS, USE MASTER CYLINDER NUMBER 1475.
THIS MASTER HAS A CASTING NUMBER 2226 821 ON THE BOTTOM, ORIGINAL APPLICATION 1968 CHARGER WITH DISC/DRUM, 10” REAR BRAKES. IT IS NICE AND SKINNY, AND THE BIG PLUS IS THAT IT HAS OUTLETS ON THE PASSENGER SIDE, AND WON’T INTERFERE WITH THE AUTOPILOT CONTROL HEAD MOUNTING BRACKETS. YOU WILL HAVE TO RE-FORM THE AUTOPILOT THROTTLE ARM AROUND THE MASTER, AND NOTCH THE TOP EDGE OF THE BRACKET TO CLEAR THE MASTER CYLINDER COVER. THERE IS ANOTHER MASTER SUBSTITUTED FOR THE SAME NUMBER WITH OUTLETS ON BOTH SIDES, WITH THE DRIVERS SIDE ONES PLUGGED. IT IS MUCH WIDER, AND WILL STILL INTERFERE WITH AUTOPILOT BRACKETS. MAKE SURE THE ONE YOU GET HAS THE CORRECT CASTING NUMBER ON THE BOTTOM.
USE 65-68 C-BODY DISC BRAKE BENDIX DUAL DIAPHRAGM BOOSTER.
FOR COLUMN SHIFT CARS, ONE MUST USE THIS BOOSTER TO AVOID BOOSTER INTERFERENCE WITH THE COLUMN SHIFT LINKAGE. THE BENDIX DUAL DIAPHRAGM BOOSTER FOR 65-68 DISC BRAKE C BOY CARS LOOKS LIKE THIS:
IF YOU HAVE CONSOLE SHIFT OR FOURSPEED, YOU CAN USE
ANY 65-73 DISC BOOSTER.
DON'T USE THE DRUM BRAKE BOOSTER, AS IT DOES NOT HAVE ENOUGH BOOST TO COMPLETELY ENERGIZE DISCS, AND WILL LEAVE YOU WITHOUT ENOUGH STOPPING POWER IN AN EMERGENCY....JUST WHERE YOU NEED IT! YES, I KNOW SOME HAVE USED THE DRUM BOOSTER, AND YES IT WORKS, BUT THE FACTORY DID USE A DIFFERENT BOOSTER, AND FOR GOOD REASON.
USE 69-73 C-BODY PROP VALVE.
RE-USE REAR HARD LINE FROM PROP VALVE.
MAKE NEW HARD LINES FROM MASTER CYLINDER TO PROP VALVE.
MAKE NEW OR RE-FORM FRONT HARD LINES FROM PROP VALVE TO FRONT FLEX LINES.
USE NEW FRONT FLEX LINES FOR 69-73 C-BODY WITH DISCS.
USE 69-72 DISC BRAKE SPINDLES, 69-73 CALIPERS, BACKING PLATES, SHIELDS AND HARDWARE.
USE YOUR EXISTING 65-73 DRUM BRAKE BALL JOINTS.
OPTIONAL: REPLACE EXISTING SPINDLES WITH 1973 C-BODY SPINDLES TO BE ABLE TO USE THE 1973 ROTORS AND BEARINGS. APPARENTLY THESE ROTORS ARE MORE AVAILABLE DUE TO USE IN VANS ETC UP TO MID 80’S
73 ROTORS AND BEARINGS CAN ONLY BE USED WITH 1973 SPINDLES.
The 73 rotor numbers are:
Raybestos PG Plus line - 7018
Raymold line - 107018
Aimco line - 7018RGS
Bendix - 141072
The 73 bearings are:
Inner - BCA - A17
Outer - BCA - A16
69-72 ROTORS AND BEARINGS CAN BE USED ON ANY C-BODY DISC BRAKE SPINDLE 69-72.
69-72 DISC BRAKE SPINDLES CAN BE SWAPPED INTO ANY 65-73 DRUM BRAKE C-BODY TO FACILITATE THE DISC CONVERSION, USING THE ORIGINAL DRUM BRAKE UPPER AND LOWER BALL JOINTS. It is recommended that one replace used ball joints with new ones.
The 69-72 rotor numbers are:
Raybestos PG Plus - 7012
Bendix - 141047
The 69-72 bearings are:
Inner - BCA - A6
Outer - BCA - A2
The calipers are identical 69-73.
In general you want a smaller master cylinder bore to reduce brake pedal effort. If you care about the pedal effort I would look for the smallest bore disc brake master cylinder.
According to The Rock, 67-70 disc brake C-body cars had a 1 1/8' bore master cylinder while 71-73 disc brake C-body cars had a 1 1/32" master cylinder bore.