I'd wager to guess that your starter is just shot. It's probably 35 years old, and has started that car thousands and thousands of times. They wear out, and draw too much current from the battery, not allowing enough current for adequate spark. And I wouldn't necessarily just get a rebuilt unit. That would probably just have new bearings, new brushes. But often the same old worn our shorted out commutator.

Get a used one from a junkyard. As has been said, a 240 starter should work. It might have an extra spade clip on the solenoid... one of those can be left without a wire.

All that said though... have you tried trading batteries? If you just get a click, but it does turn over with a jump, it could be your battery. And if you battery is too far gone, it may pull too much current from the other car to let the starter work. But since you've got it out and apart, you might as well replace the starter. Then replace the battery, because I think you need that too.

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-Matt I ♥ my ♂