Steve Graham said:All of the 4B's I've seen use hydraboost for the brakes, no vacuum pump. I can't imagine why a P/S pump from a 4B would not bolt on the a 6B.
BTW, If you do go with a hydraboost setup you will want a pump from a hydraboost system as they operate at a higher volume and pressure that a pump from a non-hydraboost system.
Steve