The first question should be, what is your intended use for the truck? Will it be a museum piece/occasional hayride wagon? Stay original, then. Will it be a working truck, doing the same jobs as a more current model? Then the biggest alteration you'll want to make (sooner or later) will be the differential ratio. If you start by replacing the entire rear axle with something from a later model then you'll have bigger, stronger brakes as well as a lower OTR engine speed, which will substantially help your fuel economy. Radial tires, absolutely, on a road truck. Tubeless tires will necessitate updated rims, but will run cooler. Bigger, better mirrors. Brighter lights, which might mean a 12V electrical system(it sounds like you might be doing that anyway). The engine is less important than any of those things, on a working truck. Here's a bad pic of what I thonk of as good mirrors. I can swing 'em out to see around a wide load.
[img]http://thumb11.webshots.net/t/59/459/9/93/66/2193993660096215731StgIlR_th.jpg[/img]
