Its caused from LACK-of-hammer'in!!
My Dad use to call it 'blowing-the-carbon-out'......
When carbon builds up on piston/in the chamber....'maybe' its raising the CR enough to cause it to 'run-on/kick-back...?
I don't think much of 'mechanic-in-the-can' stuff butt...
with air cleaner off and engine warm....dribble some water into the carb while at a fast idle.
DON'T let the engine die......keep revving it up (pretty hard) and dribble some more water in carb.
The theory is...water turns to steam and loosens any carbon on piston/in chamber.....cleans it out.
A/T fluid instead of water  may work just as well (and make you feel better too!)
Occasionally drive it around in second gear some...getting the RPM's up to 3-4000RPM .
Bring it to MB and I'll cruise with you  while you take it to 4000+ RPM going down Ocean Boulevard!
6sal6

Since you've got an automatic tranny Rudi, turn the key off with the car still in gear and your foot on the brake. It dosen't fix your problem, but you'll have no more run on.

I backed the timing back this morning but never got a chance to run it.
I need to put a vacuum gauge on it tomorrow and see if I get the carb idle circuits set.
Thanks for the help, I’ll let you know how it works out.

To clarify, if its caused by carbon or extreme heat its Dieseling.  The carbon or other hot spot is acting like a glow plug and allowing the engine to ignite the fuel/air mixture without spark.  There's always some leftover fuel/air in the manifold or even the cylinders when you kill the spark and shut it down.  If it can be ignited by other means the engine can run with the key off until it runs out of the remaining fuel (not very long, a couple revolutions).  Advanced timing tends to build more heat in the engine, so backing off the timing would be my first step as well.  Shutting it off in drive avoids this by keeping a load on the engine against which it can't continue to run.