what are the differences between the P type and J type gearvendor overdrive units ? are they just in the output shaft and housings, or are there internal differences as well ? is the main unit used in volvo applications a lighter duty unit, or are these sections the same as used in the "normal" gearvendor kits ? i realize there are different mount holes and speedometer cable locations. i am looking for a unit i can make a custom adapter from 9" or so T-601 bar stock. also, what diameter and spline count is the "normal" input shaft ? thank you for your input on this topic.