All the GPM parts are stock parts, just in metal form.
But you can mix like an off road upgrade with almost full GPM you just can't get GPM Towers or lower arms or CVD but you can get a GPm Dog bone then a gpm axel, so it will work like the CVD but it will be two seperate pieces & you will have to use the tut that was posted above & put a spring in the axel.
Hope this helps.