I have P&S steering as well, before I attached the pitman arm I rotated the steering full left to full right ,found the center and marked the steering box and shaft next to the same spot so I know when the box is centered.
the pitman arm cannot be straight down unless the steering box is horizontal with the ground-this means I had to have the pitman arm somewhat angled to the rear of the car so the steering box was centered as the wheels were at dead straight ahead, this allows me equal turning raduius left and right, but it's also only a 150" car.
another issue I dont see many address is the angle of the steering arms off the front spindles.
the proper angle should be- draw a straight line through the center of the king pin to the center of the rear end, that string line will show you where the steering arm should attach to the tie rod.
this ensures the inside wheel will always turn the proper radius of a shorter turn than the outside wheel. dragsters dont turn? ever see a car a bit loose, turn to correct and peel the front tires off? ever wonder why?