I've got a couple more thoughts for you since about 6 months ago my '70 Road Runner lost its brakes (hard pedal, not going to the floor, but no brakes).

1. My car's problem was TWO bad Inline Tube metering valve/proportioning valve (split on '70, can't remember the correct name, but the part where you hold the little pin out to bleed the brakes). The quality control on those parts is TERRIBLE.

2. You can get a pretty close to original looking brake booster (dual diaphragm) which they sell on Ebay. I had to slightly (1/8") enlarge the hole in my firewall (not visible once installed) and I did not need to buy the "heavy duty bracket", maybe because my car was stock front disc.