Distributor, distributor drive gear / Timing

I would also check the points first. Make SURE they are still where you set them. Use a dwell meter, NOT feeler gauges. A feeler gauge can easily be inserted crooked and get your setting incorrect. Once you verify the points are correct, or get them corrected, the next thing I would check is the harmonic balancer. It is very possible it has slipped if you cannot find the timing mark with a light. You should do as advised in an earlier post and time the engine up. Remove #1 plug. Using a socket and ratchet on the crank bolt, turn the engine until you feel compression coming up in the #1 plug hole with your finger. As you feel compression, look down at the balancer and you should see the timing mark coming up. Line the mark up on the "zero" on the timing cover.

Now, if the timing mark is still nowhere in sight and you have compression coming up against your finger, remove your finger and get a long screwdriver and insert it in #1 spark plug hole. Continue to gently turn the engine while noting the screwdriver being pushed out of the spark plug hole. Turn it slowly so that when the screwdriver STOPS being pushed up you will know it. Take note of where the timing mark is on the balancer. If it is not aligned with the zero on the timing cover, it has slipped and needs replacing.