Navistar used their corporate air ride on everything from school buses to class 8 trucks from the mid '80s until 2002. From 2003 until present Navistar uses an air ride similar to Freightliner's Airliner. But there is nothing wring with the "Z" spring they used up until 2003. I have so many of the "Z" spring suspensions laying around that I sell the for scrap iron. Back in the '80s and early '90s we converted a lot of spring ride to air ride. If I were to put air ride on a 2 ton, I would find a cutoff which is the frame cut right in front of the front hanger. They are everywhere and parts are still readily available. Anything you try to build will be reinventing the wheel. Here is a parts breakdown of the suspension.
http://www.truckcomponentsonline.co...ear-SingleTandem-Axle--Z-Beam_c_706.htmlI buy most of my suspension parts from these guys.
http://www.stengelbros.com/The only thing that goes bad is the air bags, the leveling valve and the bushings go bad in the torque arms.
If you know how to drill holes and can can cut the mount for the traverse rod off of the donor and weld it on to your housing, there is not a whole lot to it. We use Jancy slugger bits with a Fein magnetic drill press to drill holes in our heat treated frames,but '57 two ton frame rails are soft and will drill with high speed bits.
We use flange bolts to bolt suspensions to the frame.
https://www.imperialsupplies.com/item/0196400But I think this is probably overkill on a two ton.