Greg,
Almost all tire manufacturers have light truck radial tires (LT) that will fit the original 1/2 ton 16" or 15" wheels. As Bill said, find one that is narrow. You can check tire specifications on-line or in brochures that a retaler should have avaiable. When I was looking for radial tires, the narrowest LT radial worked on a 5.5" wide rim. Original rims are 4.5 or 5.0 and most tire companies will mount a 5.5 tire on them (although, it has been reported that tire stores in Canada will not mount this tires).
Most narrow LT radials seem to be a little wider diameter (up to 32" loaded diameter) than the original tires but this is not a clearance problem (and it gives you a higher speed at lower rpms).
My trucks have blackwall Cooper or Toyo LT radials and they appear the same as originals but they driver much better. I used tubes with plastic protectors at the stem holes. No problems in 6 years and thousands of miles (high-speed and low-speed city and interstate drving).
By the way, as Bill stated, Chevrolet 1/2 ton trucks (47-55) did not have split rims but GMC 1/2 ton trucks did have some split rims available (15" wheels, for example).
Tim
