look for headers with small tube diameters, they'll work to your advantage with a stock/few bolt-ons motor. Just from looking at summits website, flowtechs are going to be the cheapest, and they're long tube headers.
http://www.summitracing.com/parts/BIG-11508FLT/
They also already have 2.5" collectors on them, which is nice. Because a nice single 2.5" exhaust, is the absolute max size i would run on that truck.