Rack and pinion has been done on straight axle cars, but more fail than succeed at getting them to work right IMO. Problem is, if you mount the rack to the frame as the car bounces up and down it forces the spindle arms in and out, effectively steering the car (bump steer). If you mount it to the axle you eliminate that problem, but you add a bunch of unsprung weight to the car. The racks also don't look real good sitting back there.

A properly installed conventional steering box, in conjunction with a panhard bar and proper geometry usually will produce a car that goes straight down the road and that will steer like it should.

Don