INSTALLING A POWER STEERING GEAR BOX ON A '71 DEMON........2 QUESTIONS

I have my 340 and auto transmission installed on the K frame sitting on a home made stand. I plan on installing the combination from underneath.

After installing the PS gear, I found that there is a light rubbing where the steering coupler passes the exhaust manifold. I assume that once the combo gets installed in the car, there will be some left to right levelling thus increasing the clearance between the coupler and manifold??????

Also.......What is involved in changing a PS gear in a running driving car? How much dis-assembly is required to change one out?

Thanks FABO