You need to provide a bit more information than that. What type of terrain? What size tire? Engine swap? Stretch? Budget? Locked or open? What gearing you looking to run? Etc. Etc.
Personally, I'm in the process of putting in a Currie F9. Its not the Pro Rock 60, but still a pretty good axle.
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2013 NORRA Mexican 1000 - Co-Driver #199
2012 King of the Hammers - Hammerking Productions "Intern"
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