Congrats getting it running.
Yeah that timing light is not looking right at all. Maybe try a different plug wire to see if the timing light is at least nice and steady in period. Otherwise could be the timing light I suppose.
Edit: Could be wrong but I think I hear the engine sound change with the erratic light. Could be time to look at the spark/ignition side.
btw, I am no expert, just offering an opinion and diagnostic idea.
