Different Frame widths?

[jnocero]

I took a look at a 91 chevy 2wd front rack and pinion today, with a 4.3 V6. They have a smaller crossmember under the engine that doesn't carry the engine mounts (they mount right onto the frame).
The rack is bolted to a crossmember in front of the engine that is in about the same place as the front crossmember on my 67. I am going to get some measurements when I can. Does anybody know any good technical articles on what causes bump steer?
The steering column on the 91 has two universal joints under the dash to get the shaft through the firewall to the right of the master cylinder, then two more to get it inside the frame to catch the rack.
Looks like a hot rod setup.
Should be easy enough to find a 91 rack to start playing with.