Greg, as far as l am aware the later system was attached with the same type of ball/ socket arrangement as the throttle rods. It was attached under the capstan and ran forward incorporating a bushing and a spacing bracket to attach to the bellows. This allowed the rod to move freely through the bushing in one direction but still allowed the bellows to pull on the rod.

 

Greg, this is the capstan off my 6.0L. There is a pin pointing downwards on the RHS (in photo 1 ) underneath the bar that holds the pushrod pins, this is where the CC rod attaches.

The capstan and the bar move independently. On the capstan there is a wedge bit pointing upwards when the throttle pedal is pressed this catches the bar and opens the throttle. The CC operates directly on the bar and does not move the capstan.

 

The photo is a proof of concept and it worked, the CC is now much smoother and does not kick down even on hills. So I will now fabricate a better bell crank and locate it where the ignition amplifier would be, this is still temporary until I get the 6.7L engine in, it will use the 6.0L throttle capstan and I will make a bell crank to pull directly on the OEM CC stud.

 

Just out of curiosity, what was the reason to not use the computer and bellows from a Series III XJ6 or earlier XJS?. I've retrofitted one of those to my Daimler DS420 and it's a nice smooth engagement and works with the original sensor, as it's designed for 8,000 ppm.

 

With the electronic unit I have tap up and tap down. I will be converting the ignition to coil pack ready for the 6.7L and I needed to move the CC unit out of the V.

I was going to use a Rostra electronic unit but they could/would not tell me how the switch schema worked and I wanted keep the OEM JAg switches, the GM unit I used all the OEM switches although modified to switch 12volts instead of ground. this could have been accomplished with small signal relays as well. The other advantage is these CC units are plentiful and mine cost me $50.00