ltlgto, bump steer doesn't come from the box-it has to do with the steering linkage. the relationship of the of the upper/lower control arm pivot points and the pivot points of the steering linkage is what determinse toe in/out which is what bump steer is.
MIKEY--mikey is right, my reversed corvair steering box is OEM. i would never put it on a lead sled (heavy car) i would never use an aftermarket box. but the origonal aluminum corvair box works great on a light car. and mikey, you can vary the ratio by changing the length of the steering arm on the front axel.
the nice thing about the reversed corvair box is that you can mount on top of the frame and everytthing lines up-pitman arm/ steering shaft
not a good pic, but you can see the reversed corvair steering box at the bottom of the pic. i just made the steering linkage as long as the radius rods, thus no bunpsteer. they both pivot at the same angle and the same lenght/plane--thus NO bumpsteer...