Being an 83 van and 5 lugs you have the standard ½-ton rated axle, but GM gave you the spring packs out of a ¾-ton truck to up the GVW rating of your van.
Depending on the year of the 1-ton work van, you might be able to swap everything over to your 1983 van. GM has a very interchangeable amount of parts
I intend on doing pretty much the same thing with my 1988 Suburban, I intend on hauling a car trailer among other things, and feel that the 235/75/15 tires I am using aren't up to the task, they barely cut it for what I am asking of them now.
I have several axles/ parts truck suspension pieces/ and part numbers of things needed to make the swap work for what I want. I am swapping a 14-bolt 1-ton truck axle, and ¾-ton truck front suspension parts for mine. I cross referenced catalogs I have for suspension pieces and other things that needed considered and found that some of the things I have on the Suburban now can be used with the swapped parts without concern.
I will be moving up to an all season tread 235/85/16 tire with a 10-ply rating from the existing 6-ply I have now.