Good idea, check the shaft bushing. You don't need to remove the distributor, just see if the shaft will move side to side any noticeable amount. If so, replace the distributor.

At 20 degrees initial timing, you'll lose power in the top end at best and damage the engine at worst. That's with a normally spec'd A-series distributor. With custom re-curved distributor it may be different.

Yes, weak spark can cause erratic timing. Or more correctly, what is causing weak spark can cause erratic timing (worn bushing, incorrect points gap, etc).