http://www.madenterprise.com/scparts.htm

that has pretty much everything you need to know for pricing out a s/c conversion kit. it will hands down give you the most power out of that truck!

there's not too many mods you can do to the N/A and keep it N/A and put down much more power. You'll probably gain a little bit by ditching that flowmaster exhaust for magnaflow or bassani. Flowmasters are known to eat up some power on these trucks. You'll pick up a little by doing 2 high flow cats in place of the 4 stock cats, can do an E-fan, port the throttle body, intake, valve body (or separator plate), and a chip/programmer. The programmer will take your speed limiter off, but they dont really do much for performance for the N/A's.

Anyway, you could spend 3-4K on every N/A bolt on mod and barely make a big impact in performance, or you could spend 3-4K on a top end s/c swap and it'll be a whole different monster! the swap really isnt much more than a manifold swap!