Odd timing problem 360

Try a different timing light. If the mark is moving, disconnect the vacuum advance. If you dont have one or it doesnt change, look for play in the oil pump drive shaft. If there is any lateral play (like DGC said... Check this by using a large flat blade screwdriver and try to wiggle it side to side, not twisting..) then replace the drive and the bushing at the same time. They wear together so if the bushing's bad, so's the drive.