Depends on what size Silverbacks you thinkin about gettin and I would just change out the secondary spring on you stock clutch. it would be a whole lot cheaper. 28" silverbacks - Lime Green secondary spring. and if you wanted to go 30" or 32" Silverbacks i'd go with the Yellow secondary spring. I believe they're made by EPI. My local atv carried the Red that i use but you can go online and fine one easy too.
2008 Kawasaki Brute 650i
2" Extreme lift
29.5" Outlaws
12" ITP SS 112S
1.5" Spacers
EPI Red Secondary
EPI Maroon Primary
M.I.M.B Snorkels
Warn 2500lb