If you can arc it with the screw driver and it cranks, it's probably everything in between. Solenoid? Main cables? Solenoid wiring? These cars operated for 40 years with the same old starter.
But the wiring is getting tired(internal corrosion)
I usually bump up main cables to 1 gauge, solenoid wiring to 10 gauge, and usually buy a new solenoid(if it's mounted elsewhere). This seems to be a very common and occuring problem nowadays it seems.