Power Steering Woes... :(
On my 73' Duster all I had to do was disconnect the steering coupler and the steering shaft simply slid back a couple of inches towards the firewall. MY PAW 99 dollar headers sit pretty close to my box as well but did not have problems installing them with box in place if memory serves so that means it should come out without dropping the header. Will yours? You get the joy of figuring it out:)
Never had any heat related problems with my box from headers, do what it takes to get the job done and keep the power steering. I prefer to get my work out at the gym not behind the wheel.
Pretty much anything you have to do on these cars around the headers is challenging. Still beats running A-body manifolds.
Also, if it's just leaking around the pitman shaft you probably could change that seal out with the box in the car.