Fishy and Trailbeast were invaluable when I did my 904 , I bought a forged drum with a relocated groove with my kit and was able to get 4 thick and 2 thin in it , 6 are better than 5 eh LOL , most people I spoke with before doing mine said they had to machine their drums so I figured it was worth the extra cost to just buy a drum designed for what I wanted to do , the mixing and matching of clutches allowed me to avoid the search for the proper snap ring and pressure plate combo . 3 years and a lot of beating later it still shifts strong without slipping .