They do have hubcaps that are different from the 1/2 tons, they are specific to the 3/4 and 1-ton models. The originals are fairly rare and expensive, there are re pops available but they are also expensive. Attached is a picture of mine for reference, I bought chrome off eBay and then filled the dents and repainted them in white (refrigerator enamel) GMC branded are even more rare but they are available.
https://www.flickr.com/photos/advance-design_parts_co/8129054429/in/album-72157631867396207/You will need to drill and install clips to make them accept caps, they do not attach to the wheel without them. I have some step-by-step photos I can post if needed. I installed four per wheel and adjust them occasionally to keep them tight.
