The run-on is most likely misadjusted throttles or idle speed too high. Higher octane fuel would cure it but that's a waste of money for a problem that can be cured by adjustment.

Ignition timing is dependent on when the points open, as they wear, your timing will change. This was exactly the reason manufacturers needed to go to electronic ignition to meet US EPA emission standards back in the early '70s.

Ensure that the point gap is set correctly before checking the timing. You can set the timing without a light but you'll need to know which way the distributor shaft rotates. If you don't have a service manual, you can find old ones in most libraries to find tune up specifications including which direction it turns...or you could simply turn the crankshaft clockwise or have someone operate the starting motor and observe the distributor shaft.

Start by turning the crankshaft pulley (clockwise) until the crankshaft mark lines up exactly with the appropriate timing mark. Then, position the coil high-tension wire about 1/4" away from engine or body metal, loosen the distributor clamp slightly with a wrench and turn the distributor body WITH rotation until the points are visibly closed. Turn the key to RUN (don't crank it, and be sure it's outta gear just in case you do), turn the distributor SLOWLY until you hear/see the spark jump from the coil wire (don't put your hand near it, there's 20-35 kv in that spark). Leave the distributor in that exact position and tighten the clamp bolt. Turn the ignition key OFF, install the rotor and remount the cap. Reinstall the coil wire into the centre hole of the distributor cap.

The engine is now (closely) timed to specs.

Method 2: Beg,buy, borrow, steal a timing light. Connect as directed. Start engine. Loosen distributor clamp. Turn distributor as needed until crankshaft pulley mark lines exactly with correct timing mark. Tighten clamp bolt. Shut ignition switch. Count fingers. Disconnect light. Close hood and drive to 7-11 and get coffee.