Also, would check out the specs manual on your truck, Gary has wonderfully documented it. Are you looking for a tire that looks like the old ones, or a new tire? Radial or Bias Ply? Just some factors. Like.i said earler, might want to check the spec list and see what was origianlly offered to see what a good starting point is.
Hunting for a Bullnose, single cab, 8 foot bed, decent shape with little to no rust! and under 10k in near or around the STL Mo area, (Illinois is a valid option aswell!)