I've installed a bunch of South Bend clutches at work (not many in a Duramax but lots of Cummins), and they are good clutches. They have excellent customer service also.
The dual discs all come with new solid flywheels. I've run 2 south bend dual dis in my truck, one sprung ceramic and one unsprung feramic. Great clutches.
Make sure you if you get a double disc get it strapped... my ceramic is not and its loud as hell when you have the clutch pedal in, wish I knew about having it strapped before I paid to have it put in.