No clue on the 400. But the biggest thing to deal with on a true dual exhaust is the fuggin big a gas tank taking up basically driveshaft to frame rail on the driver side. That's what's keeping me from doing Duals ATM. One thought I had was to get a fuel cell put where the spare tire goes. But there goes the spare tire.... It's like dominoes with trying to move things around. If I had a K1500 I'd build a roof rack and plop a bigass spare up there for that prerunnerish look. But alas mine is the C1500... I'm getting more OT here but I've thought about getting a toolbox and hiding a tank in it, especially if I bag the truck. It would be different. I think a gas tank or tire in the bed looks tacky but yeah I've gotten away from dual exhausts rambling on now. Iirc there's not enough room beside the driveshaft on the tank side to run duals near it like a 80's corvette. I could be wrong but I'm nowhere near my truck and if I were it's too friggin cold for me to go look. (11 degrees F)