You can certainly run a 3.5 with headers..hell, I've seen people run 3.4 with no knock without headers. It's all about the tune and the individual car.........
*dismounts the soap box*
Welcome to the community. My best advice would be to branch out and look at other forums like gpona.com, and clubgp.com when doing research about new mods. Don't log into that "safely modding" thread and treat it as the bible of modding, it's far from it.