Keith,
If you'd like I can provide a fair amount of detail on how my cable shift is set up on a standard G50 tail shift. It uses a Toyota shifter and Morse stainless cables. The shifter's fore and aft motion is a direct transfer between the cable and the external shift rod and the torque of the shift rod is done through a bell crank affair.
I am sure that any number of cable shift shifters could be used. For instance, while I was putting a new boot on my Stealth (Mitsubshi 3000gt), it was apparent that it did the same thing as the Toyota: provides direct fore and aft motion from the shifter bottom and translates side to side shifter motion to fore and aft motion that can be delivered via the cable. One only need to verify that the direct fore and aft motion is adequate to move the Porsche shift rod through its full range of motion and provide the proper bell crank ratio to turn the shift rod through it full range of twisting motion (this includes that little extra for reverse that threw me on initial set up when I didn't recognize that there was a bit more clockwise motion than I had accounted for.)
Regards,
Lynn