Here is the details of the auto shift indicator.
This one here is from the 1980-82 digital cluster that I am using.
It is horizontally positioned. If you are fabricating a panel for aftermarket gauges, then all you need to do is cut about a 2" x 3/4" rectagle in your panel face. Leave room behind it for the entire shift indicator mechanism to be installed. It will mount against any flat surface and have it's own lens.
When you are done, you can run a small LED light with wires attached secured with the adhesive side of velcro directly to the back of the shift indicator to provide illumination.
In reference to the pictures below, the first picture shows the actual window size that you need to cut out. Measure it for yourself to be accurate. It is approximately 2" x 3/4".
The second picture shows the back of the shift indicator mechanism. The red circles are the plastic pins that have to be worked or snapped loose to remove it from the original gauge panel face. You will not need to mount it this way for your new panel. The entire thing mounts flat against the gauge panel so this will work for any gauge panel that you are using or fabricating. When you mount the shift indicator, apply a couple of small drops of super glue between the ends of the clear lens and the white backing support.
Depending on what material you use for your panel gauge, whether it's metal or plastic, you can use either silicone adhesive or super glue to hold it flat against the gauge panel. Be careful not to get any glue or adhesive in the area that will show through the opening in your gauge panel face. You will probably need to improvise securing the support for the cable sleeve where it comes to the panel. One option may be to get some velcro with very good adhesive (not the cheap stuff) and wrap a piece of that velcro adhesive side down against the cable so that it wraps it then the remaining velcro around it can be stuck against a flat surface. Another option is looking to see if a tie wrap will secure it.
In the picture I have the cable and sleeve removed along with the support for the cable sleeve.
You you look at the next set of pictures, this shows the cable sleeve and support in a 1985-88 standard digital cluster.
Looks fairly reasonable to me, thanks Watchdevil!
Here's the rest...
The horizontal shift indicator mechanism is virtually identical between the 80-82 models and the 1985-88 models. The only difference is the support for the cable sleeve which is slightly varied in design. The support for the cable is circled in red. You can also see the rest of the cable and the collar that goes around the steering column. More than likely that collar will be broken if you find one. Don't worry. A regular zip tie wrapped around the entire collar will tighten it perfectly around the steering column yet allow movement so you can adjust the needle in the readout so it will read correctly depending on what gear you are in.