I"m not sure on your particulat truck, which brakes you have in the rear but, the manual for the 55.2-59 chevy 2-ton brakes says to back off the adjustment on the top shoe on both rear wheels before you bleed. Looking at the way the cylinders are situated on the backing plate, of you don't do this, it will trap air in the top of that cylinder. You might look through your manual again and try that.
Also, if the fronts are not engaging at all, the pistons in the wheel cylinders may be frozen. They will bleed fine but not move. You may need to pull them apart and put kits in them or replace them altogether. I'd do that before doing any more bleeding since you will have to re-bleed once you mess with them.
