going back to manual disc brakes from power

Professor Fate said
If you're going to the 2 bolt master, you'll need the adapter plate for the swap.
Mopar Master Cylinder Adapter
That adds depth to the master mounting point, which means your stock manual pushrod is no longer useable- you'll need the adjustable pushrod to gain the extra length (or modify yours if you're feeling creative).
Mopar '62 -'70 Adjustable Master Cylinder Push Rod
I don't believe the bellows ever came on a 2 bolt master, and the adapter would probably not allow use of it anyhow.
The adjustable pushrod comes with the rubber bushing that locks the pushrod into the master.

The original brake pedal push rod works just fine with the 2 bolt master cylinder and adaptor.

1973dust said
Thanks, I also have the adapter plate coming. Dr Diff's description claimed the original rod would work but I won't be surprised if that's not the case. While searching, some said it's fine and some said you need an adjustable. It seems nothing is ever easy in Mopar-land.

The original push rod works just fine. I have an original manual brake pushrod in my Duster with the DoctorDiff 2-bolt aluminum master cylinder and adaptor with a 15/16" MC for manual disk brakes. The pedal remains more or less in the same place as with the factory MC.

Bewy said
Post #13.
I suspect the m/c size would be the other way round: 15/16" for manual, 1 1/32" for power brakes.

Nope.

Stock A-body master cylinders were 15/16" for 9" drums, 1-1/32" for 10" drums, 1-1/32" for manual single piston (73+) disks, 15/16" for power 73+ disks, and 1" for the KH disks. From the '73 service manual, "V-L" is the A-body designation. The 2.75" calipers were B/E/R/F/M/J body fare, pin style in '73 hence the "floating" designation, the 2.6's were A-body single piston slider calipers. Since this chart is from a '73 manual it doesn't include the '76 A-body 2.75" piston sliders, but they used the same MC as the 2.6" calipers on A-bodies anyway.
From the '73 FSM

From the '70 FSM for the KH brakes

As you can see, A-bodies are actually backward when it comes to manual and power disk master cylinder bore sizing. That's because the power booster linkage changes the pedal ratio (A-bodies use an angled power booster bracket). So the power disk cars actually got a smaller bore master cylinder than the manual disk cars.