I have not heard of rubbing tires because of a power steering box install. I have heard of that on disc brake install. Are you confusing the two? I assume you have that install done and have solved any rubbing and adjusted the stops.
The problems I've heard of talk about the actual install. Bolts lengths, welding, etc. Use a plumb bob and any other devices to be accurate. Try your darndest to decide what wheels now. Buy the box. Mock up the column. Try to mock up the box with clamps, straps or tack welds or any method and check it out. Do this with front axle off the ground and tires off so there is no load while testing the mock up.
As far as attaching the column shaft to the box, that is phase two. Keep an eye open for problems with this phase during box install. That part is: what is on the box to attach to, and what is sticking out of the column to attach to. The key to this stuff is the accurate mock up. Most of us only do this once, so not much experience. Just one experience that had this or that problem, which you may or may not have. Think it out and go slow and read the instructions and the web. You will be just fine. Mock up, lightly attach the pitman and get some steering action by turning the box shaft by hand to see if all is well.
