Ok, I tied my solution but there is more broken then I first thought. I think my clockwork is not salvageable -_-
Here is what I tried:
The capacitor in the clock I got from Dave was burned. That happens when the car is standing for a long period time with the battery connected. When the battery is very weak, both contact points are connected and there is not enough power to wind up the mechanism...
The capacitor in my rotten clock was still good, so I swapped it over.
But there is a thin metal clip on the "new" clock that's broken off. It stabilizes the mechanism from tilting and shorting.
This part of the clock is pressed together, so I can't fix that clip without breaking the whole thing.
I call this repair attempt a fail and now I'm trying something different.
If you have the same issue, Dave, you can try this repair. Maybe it works for you?!
Another option is to use a Ford clockwork, they had the same Borg Instruments mechanism and they are available, but not cheap...
http://omicronclock.auctivacommerce...ovement-Repair-Kit-OEM-1965-1966-P161129.aspx
I also found this conversion kit, but it's not cheap too...
http://www.ebay.com/itm/Quartz-Conv...VD-/371193826743?fits=Year:1969|Model:Mustang
I will try to retrofit a modern radio-controlled clockwork. Something like that... I hope this works!