rstardark: You might think about reverse engineering your question.
How do you intend to use the truck? Is it going to pebble beach? Is it going to the lumberyard and gravel pit on Saturdays, or might it be a little of each world?
They do make custom and aftermarket frames for your truck that are all setup for IFS, small block, and other modern conveniences. The S-10 is one of nearly infinite chassis swap options for your truck if you decide to go that route. Again, the '58 original frame is considerably heavier and more truck like than the newer S10 frame and then you will have countless issues of fit on the conversion to a modern frame. How will you use the truck? That will help you decide which way to go.
Powdercoating is an awesome and highly effective process and coating, but it comes with considerable effort and cost. Rustoleum black is an awesome and highly effective coating, and it can be done in your driveway and/or garage with great success. The rusty metal Rustoleum, IMHO, is a very very good product.
Take a wire brush and knock the loose stuff off and scratch the frame down as much as possible and then either send it out for a $2000 powdercoaring job, or get $30 worth of rustoleum and go for it.
In either case, the merits of each approach are noteworthy. You can beat powder coating with a hammer (or rocks off the road) and it generally won't fail. You can beat rustoleum with a hammer or rocks, and it will chip, but then you can easily get under there with a touch up brush and cover the chips. With powdercoating, if it does fail (HIGHLY unlikely) and you decide to fix it, you will have to go back to square one; send the frame out again.
