Excellent, thank you!

 

This may sound like a dumb question for you Gorn, but would any of this have to due with the ground locations being painted due to the restoration? If a simple film could cause a problem, can the thickness or quality of the paint have to do with the ability of electrical flow? Do you need bare metal connection for a ground or other connections? I know this would not explain the intermittent problem, but could it possibly play a part.

 

A bare metal contact is best. OE connection of ground cable on a ‘69 is the upper alt bracket and it’s bolted to intake and uses a water pump bolt.
I suggest moving the cable to one the two holes on block below alt next to timing cover after cleaning paint off the boss and run a tap for thread cleaning.
Add anti seize to bolt threads when securing cable. This method/routing connects battery to block just like the starter.
The electrical section of ign switch is mounted on the lower section of steering column and it may need some adjustment making a complete connection when slid into place with key.
The unfortunate action, with any electrical switch, is arcing between the two mating contacts when they are close physical position. This action, performed several times, will leave carbon buildup, this now adds resistance to the circuit - bad over time.
Good luck