On a small block, there's a bushing in the block that wears out and causes dist. wobble. It's cheap, but can be a pain to change. Look down in the dist. hole an see if it looks out of round.
The bushing in the block supports the oil pump drive shaft. If it's worn you will get excessive wear of the drive gear and cam gear. I could see it causing timing variations but not dwell.
I vote for slop in the distributor shaft. You can check by grabing the rotor and try to move it side to side. If you feel play it's time for a new distributor.