Eric
I can tell you that most of the replicas I have seen use different pivots than original, and different than each other. The most common I have seen is a steel tube welded to a pair of plates...one at each end which are then glassed to the body part, this allows the clip to hinge around the tube which usually sits in a pair of pivots (I use urethane anti-roll bar mounts.) A simple shaft collar on each side keeps the part from moving side to side. As far as the width of the pivot points they could be anywhere, but the wider the more stable. This setup is used on the GTD cars front and rear and allows for quite a bit of adjustment as the pivots can be shimmed up or down, and slotted holes will allow fore and aft movement...I hope this helps, but if you need I can give you dimensions off a GTD chassis, just don't have them right here at hand.
Good Luck
Phil