My '57 Panhead came with internal throttle ad spark advance cables. You can get the bits from antique cycle supply. The grip has an internal thread that engages a stud attached to an internal slide that sticks through a slot in the bar. Twisting the grip screws the slide in and out, pushing and pulling the control cable.
http://www.antiquecyclesupply.com/As long as you keep it lubricated, the system works quite well.
