Rack and pinion

Back in the day there was Uni-steer but I think they got sued out of business because they tried to make the rear steer work with a rack. You really need your steering to be from the front of the spindle for a rack and pinion. The only way to do that is to to do the whole enchilada and get a coilover suspension with the Mustang II spindles.
Save up or abandon the idea. No other way.