I wanna put some custom exhaust on my truck. It has a 350 and is stock right now. I'm thinking about getting some headers and running straight pipes off those. Will this affect my trucks computer or anything like that? What will give me the best power, mpg, and sound? Should i run single or dual? Out the back or out the side? What size exhaust? I've heard that a cross-over pipe helps too? I know this setup will be illegal and loud but i live in Montana and the cops don't care. What are some over cheap, simple mods i could do for better mpg/power? Thanks for any help.

This is a Canadian truck. Though, I'm pretty sure that other than the gauges everything is the same.