I've seen a rack and pinion setup on a semi truck front I-beam axle at a trade show, looked interesting, but I'm not convinced it's a good idea.

The normal Steering gear boxes, particularly Saginaw with the ball screw and rack and sector (not a "worm box") that has the integral PS valve and a cylinder or two work just fine, and are cheap and easy to work on.

Stick with a normal PS gear box.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-