Ditto, keep the worm gear. A rack woudln't work very well with a beam axle anyway, as you would have to have some sort of way for the steering shaft to not only flex with the suspension motion, but it would also have to have some sort of plunge joint to accout for the length changes during that motion (like a driceshaft does). Nevermind the fact that available racks would be far too light to handle the stresses. That's wht you don't see them on anything larger than 1/2 ton. They're just now starting to use them on 4x4s, because of the strength issue.
I would like to note, rack cars do not run any more caster than cars with a tradional steering box. Average caster setting is rign at about 2-2.5 degrees. It's not unusual to run a car with a steering box at 3-4 degrees. Trucks do tend to run deeper, regardless of steering system, 3.5-5.0 degrees is common.
