Remove the MC from the booster
Remove drivers seat
remove the clevis pin on the brake pedal to the booster input shaft
remove the 4 9/16 nuts holding the booster to the firewall. Use a long extension, wabble joint and deep socket. Its a PITA to get to, thats why you remove the seat, gives a LOT more room.
When you put it back together be SURE and get the clevis pin clip back on. If I have to ever do this again, I'll drill the pin and put in a cotter pin.