I used 2 1/2" cuz I have a lot of that stuff laying around, but it really shouldn't matter cuz it's not flowing anything but sound waves. I put them all after the muffler and just routed the 32"'s where ever it would fit and capped the end.

Example



My Dmax, worked on it too.

 

I may have to try that. I don't mind noise, but drone and rasp are annoying.

 

I redid my exhaust on my turbo truck 5 different time and always had highway drone. I tried everything, insulating the back of the cab and floor with dynomat, different mufflers, duals, big singles, but nothing worked like the resonator tubes. Dropped 10 dB's at cruze according an app for my iPhone. Nice and quite cruising but when you step on it, gets louder!