master cylinder interchange

Lyle, you can use a Ford MC. I'd try a 68 or so Galaxy with front disc brakes. Just remove the residual pressure valve from the rear outlet. 75-78 Matadors used a 1-1/8" master cylinder. 71-74 Ambos with disc brakes used a 1" bore MC unless they were manual (Ambo would have been all power brake cars), then they used a 1-1/16" bore. So I think you got Matador and Ambo confused -- last Ambos were made in 74.

71-74 were Kelsey Hayes brakes, 75-78 were Bendix with large piston (big cars, 75-76 small cars -- small cars changed to a smaller piston caliper 77-78).

I can answer my own question.  I pulled a wheel and measured and they are still the 2 inch wide in 61.  I bought the car for the engine and hoped the brakes might be wider also.  Oh well, So far the engine appears to be a great buy.  Are the spindles or A arms the same as my 60 American?

The LOWER A-arms are actually the same, the uppers are different. AMC has a separate part number for American and Classic lower arms, but the only difference is the inner bushing. Classic uses a bolt, American a much larger bar in the rear. I think the Classic/Ambo bolt is 3/8", the bar on the American 1/2". When you bought an arm from AMC back in the day it came with the bushing. The lower trunnion is the same also. Upper trunnions are different.

The 64 Classic had wider brakes. The 61 Classic six might not be wider, but the wheel cylinder is a bit larger. Don't have my books handy so can't check anything right now. You need to check your American. It might have 1.5" or 1.75"wide front brakes, not 2". Check diameter also -- the Classic might be an inch more in diameter but same width (9" or 10" vs. 8" or 9"...).

FYI,
The master cylinder does bolt up but on installation today it interfered with the pin bushing and bale wire. The booster is a Cardone and the original AMC booster did not have this bushing. Cardone stated they rebuild boosters from the pile to fit the request so the booster I received is built to AMC bolt dimensions but was not an original AMC booster.
Long and short I fabricated/installed a 0.125" spacer and re-measured pin length and 0.990" was the number I used from the front of the spacer.
Pedal travel is 1.5" that I was aiming for.