I just received the 1st of 2 clocks I bought which are genuine 767!
I already tested it, it's been quite easy: as you can see in the following picture it has 2 28VDC feeds:
One coming from the HOT BAT BUS which powers the clock time base only and one from the BAT BUS which powers the logic and the displays
there is one ground per feed and one chassis ground.
Plus there are the feed and return for the backlight, the ARINC channel to send the GMT data bus and the remote controls from the glarewing panels to start and stop the chrono.
Following is a video of the clock in action...enjoy!