Could always split into dual pipes after the cat if you want the dual exhaust look. Or you could run two cats and have duals all the way down. Muffler choice is personal preference. Goto the various companies sites and listen to them.
Glasspacks are cheap, loud and mean! Of course you can shell out the money for some turbo-mufflers but it's only an 85, and it has differnet color fenders. So I'd say go for the cheap route and put glasspacks on. Split the pipes after the cat and run duals through glasspacks to the back. I dont know what that would do for cab resonance? probably a bit too loud....