I am trying to install disc brakes on my 70 duster that currently has drums. I have a complete power disc brake setup from a 76 dart. My question is about the power brake booster. The bolts on the back of the booster are spaced further apart than where the current manual master cylinder is mounted. Are all the power boosters the same mount on the back? When i checked the photos on rockauto.com, the different years looked the same. Just wondering how to add the power booster to my firewall. I guess i could just run manual disc brakes, but i would really like to use the power.

AFAIK, the A-body power booster setup was the Midland-Ross unit which used a bracket (which held a 1:2 ratio-changing link) that went between the booster & the firewall. That booster doesn't bolt directly to the firewall.
See this link -it's a performance parts site, but has a decent pic of the general booster/ bracket design. (I'm sure Dan has better illustrations) I would suggest you get a factory service manual, which goes into much greater detail.

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63 Valiant Wagon
225 - 4 bbl

You do need a bracket which spaces the booster forward and upward relative to where the nonpower master cylinder mounted. The bracket also holds a series of levers and pivots, the lower end of which connects to the brake pedal (in place of the nonpower master cylinder's pushrod) and the upper end of which connects to the input rod of the booster. There is no "the" A-body booster. There were at least three different ones in the '70-'76 timeframe.

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Too many people who were born on third base actually believe they've hit a triple.

Thanks for the advice guys. I guess i left that stuff behind when i pulled the master/booster combo. I guess i will be running manual disc brakes!