Also, regarding the other brands Exedy is currently redesigning the 6 bolt twin disc as they didn't hold much over 400 ft/lbs and I have heard numerous horror stories in regards to the Clutchmasters so I would stay away from those two.
Carbonetics just released a full carbon twin disc for the 6 bolt application that looks to be an awesome piece, but it is VERY expensive.
And time for a shameless plug...
We also happen to sell all of these at some very competitive pricing
Chris