Engine won't stop running.

I have my 63 170 running pretty good. All new electrics, supplemental electric fan for the radiator, rebuilt Carb, new head gasket, added a PCV valve with the down tube sealed up, new starter relay cables distributor points and condenser, etc. It is the weirdest thing, I'd say 1 out of ever 15 or 20 times I turn the key to stop the engine, it doesn't stop! The switch will just turn back and forth from Accessory (which never worked for me) to on with no effect on the running of the engine. It is not spinning in place, it appears to definitely be clicking thru each position in the switch. Once I popped the clutch to stall it out, but then the oil and Alternator light come on because of course it is still "on"! It has only happened 3 times and Eventually I can get it to turn off.

Obviously sounds like the ignition switch, but do they act up intermittently like that, or do they just stop working? I tried to see if there was already a post about something like this but couldn't find one. I did see how to use the paper clip to get the tumbler out which is VERY helpful.

Do you think I should just switch out the ignition switch?

The switch is probably the problem. And yes, ignition switches will work sometimes and then sometimes not. Eventually, it will quit working altogether. Start with the switch and go from there.

Also, check your plug-in at the back of the switch to make sure that the plug is clean with no wires crossing before replacing the switch.

my guess is it's the ignition switch..

Yep, ignition switch.
You can try spraying it out with electrical cleaner, but that is only postponing the required replacement.

I will say that electric fans can cause feedback, and charging systems can also keep things running if they feedback, but your excellent description pretty much rules those out. In both cases, the lights would go out when the engine dies.

Thank you, as I suspected. New switch is ordered. No need to deal with it when it is inconvenient.