This kind of mod would allow you to completely fix bump steer:
Power steering rack setting bump steer at ZERO:
http://www.rc-tech.net/pantera1/index.htm
Here is a Pantera Rack in the middle, the MGB rack on bottom, and the power MGB conversion rack on top:

I extended the end but left it adjustable till I found the Zero bump steer point...then welded it in place. Since MGB joints are rebuild able it makes it possible to pull apart and weld without damaging the joint:
