I have a 62 page "slide show" training document from Chevrolet showing how to overhaul truck steering boxes. It is dated 1952, but I'm pretty sure the procedures would apply to your '58 box. I've attached a few pages. Each page is a separate .JPG file. Average size of a page is around 140 KBytes.
I could email 5 or 10 at a time to anyone interested, either for their own use and/or to publish on this forum.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
