Rear Steer Rack and Pinion

Rear steer rack shouldn't cause bump steer. Its moving the rack to the front that causes bump steer. Simply switching the lower ball joints around doesn't work. There is a old thread here with lots of info about front rack and effect on steering geometry.
The most effective method fo attaching a steering column is the same way its done in other cars, first universal joint under the dash. That means altering the steering coulmn, altering the lower mounting plate, firewall, etc..