I have just complete the same conversion on my 1968 Camaro. Under the dash on the brake pedel assembly are two holes, the upper one is where your manual brake rod now connects, and the lower hole is for the power brakes. You may experience problems removing the the pin from the upper hole as it is enclosed in the brake/clutch mount housing, but this is easlily overcome by removing the pins that holds the btake peddle in place and lowering the pedel enought to remove the clevis and pin , then re-install the brake pedel.
When installing the power booster you need to ensure that you adjust the rod going from your booster to the brake pedel to the correct length so as to not damage the power brake booster. A dry fit does not take a lot of time but it is time well spent.
Also the power booster moves the master cylinder out from the fire wall you may need to have some new brake lines fabricated as as everything fit properly.