I'm not aware of any disk kit for the early 3/4-tons that doesn't convert to 1/2-ton brakes at the same time, so that would argue its not an option. Last time I looked it was in response to someone else's similar question and I could not find anything.
But aside from that issue, if they are narrower its not by enough to solve the problem. They are almost interchangeable, one truck to another, so the difference would be in spindles and hubs and isn't likely to amount to much.
