You would be surprised by how many vendors do not "do their homework" when they offer a product. As Bill and Grigg mentioned. It is not a good idea. Even unisteer has one, however its a single sided rack that mounts to the frame and still requires the tie-rod between the spindles. That would be my choice if you really want a rack on a straight axle. Then again, if I went with a straight axle, I would simply have bolted a power box to the frame and have been done.
Yes, todays modern Class 4 and larger vehicles have rack and pinion on larger Arvin Meritor and Eaton axles. Then again, the wheels and tires also way 300# each. While the geometry may be similar, the physics is different.
