I know if the shaft that controls the butterfly is worn, the engine will have a tendency to run lean at times, rich at others, making for unstable performance. Some get so bad that the only good fix is to have he shaft machined and bushed, making it tight again. Also, like the earlier comment, if your car has a vacuum advance on it, it is the wrong distributor. That was only used on 1974 tii's.
Good luck, it will work out.