Just taken a mk 2 clock apart prior to installing a circuit board and micro processor , wish me luck !
You say Your original clock mechanism will be uProcessor driven ?!
Some kind of kit or a diy ?
It’s a kit , supplied here in the UK .
The clock will be fine if you just clean up the original mechanism.
I once bought a box of Jag clocks, all NOS and in their original boxes, that were from XK’s thru early E’s (both pos. and neg. ground). I went through all 2 dozen and could not get any to work. I figure they were all from a dealer and the bad customer returns were placed in the new replacements boxes and stored for many years.
Phil.
Don’t suppose you have any left ???
That’s a pity. I guess you are quite right about them putting the faulty ones put back into original boxes. It would make it very difficult to tell the faulty from the new! 
I was told some time ago that they have two magnets which become a bit dirty or corroded quite quickly and that a good, gentle clean is generally all that is required to get them running again. Others will know if that’s true or not. I guess most gauges in these cars are guides rather than accurate instruments. I found that out the hard way when I discovered that just under 1/4 full on the fuel gauge meant empty! I then discovered how heavy a MK2 is to push!! 
Tim
The consensus among clock experts , is that it is the contacts that give trouble in these clocks . I never found any magnets , maybe that was the bit that fell on the floor !!! But I do have the unwanted contacts . Going to finish assembly and test it today 
Well , the mk 2 clock works again , and the mk7 one is now in pieces . But I discovered that one of the solenoid wires had become disconnected , that didn’t help it work !!! As the mk2 one is a spare , I will take the solenoid from it and stick it in the mk7 . Then that one , after regulation , can go back in the car .