You already have the best upgrade you could do for a WJ (the diverter

). The WJ isn't going to be the limiting factor in running 60's. The weight and the shape/condition of the bottom will affect your top speed more than the pump.
Personally I would recommend using the money you would spend the Berk on engine upgrades to help performance & longevity (a good intake, carb & cam combo, improved ignition system, roller rockers...).