What is Needed to Convert Manual to Power-Assist with 9-inch Drums

yes ,they were.I had a 65 Valiant in the late 80's with all original power drum brakes and they were 9 inch .It had a 170 cu in slant with an automatic . You just need the booster and the right pedal assembly that goes with it . It's a goofy thing that offsets the master & booster so it will fit.Same as the one used on the v8's of that year.