can convert the clocks, but they arent cheap by any means.
I have one of those Abbot-X boxes if you're interested ? I used it on my car for a few years until I ditched the old mechanical clocks.
Mine has a short cable, about 16" long to old Ford clocks fitment. Again, the cable I had made by speedycables.
Abbot X werent able to supply me with one as they werent familiar with the car.
On my car it worked fine up to about 100mph, after that it stopped working. Not sure why, might have been the cable route was too tight and too difficult for the motor to turn, as in order to fit it behind my dash, I had to do a full 180deg turn
Also read this thread. Not sure if they ever got a working unit yet.
Only other option might be to see if the box can be converted for a mechanical output. Not always easy though.