Dynomax makes true dual kits for your truck for $100 or so. Just call Jeg's, add two of your favorite mufflers, and you're good to go, it's a straight bolt on. Ditch the cats if you can. Mine were gone before I got the truck, I added the dual exhaust kit and a set of headers. Sounds great and actually helps performance significantly, unlike a cat-back kit which IMO is a total waste of money unless you replace the cat, crossover, and all the exhaust tubing to a bigger, mandrel bent size. Good luck. I'd just put duals on it.
Tim
'84 Chevy K10, lifted, loud, fast, and 3/4 ton axles