I got the SpeedCal installed last night. I ended up drilling a 3/8 inch hole as far forward as I could on the drivers side of the shifter. The 3/8 hole was a perfect size since the plastic protective sleeving over the wires just barely fit through, and it was tight enough to keep the wires from moving around below. If you drill the hole too far aft, it may interfere with the linkage. Not that I drilled one there by accident.

I have a picture, but can't figure out how to post it. The only problem that I had was that I needed to remove the connector from the grey and white wires to get it through the hole. For that I needed to pull out the red lock, release the wires and pull. The only other thing that I did differently was to tap into the switch 12V wire (purple and pink?) that goes to the convertable control. That way, there is not power to it all the time. The wire is there for the coupes as well, it's just not used.
Anyway, after I got it installed and set the switches, I took it for a test drive. Using highway markers, I measured 14.7 miles for a 15 mile run. After readjusting the switches for a 2% correction, the readings were right on. There was less than a tenth of a mile difference after 18 miles. That's less than a half a percent error according to the odometer and the mile markers and that's close enough for me.
I need to get back in there for the primer since I just now saw your last post WYTSTANG.
Thanks for your help and Happy New Year.