Our boxes are built specifically for us by Lee Engineering with recommended valving based on his extensive experience. The 670 boxes are initially built on an assembly line with questionable tolerances, which is unsatisfactory for Tom Lee and ATS. Every brand new unit is completely taken apart, re-honed, blueprinted, re-valved, dyno tested, magna-fluxed, and finished in a zinc plating. You will not find any rebuilt used box, or factory assembly line 600 box that can compare to Lee Engineerings 39 years of steering gear experience. These are race proven precision boxes, built exclusively for ATS.