Did you use a timing light at about 500 RPM with the vacuum line disconnected? At what deg. mark did it run better? I think initial timing spec. is 6 deg. BTDC for that car.
Rev the engine to about 3K and watch the timing mark/pointer. The mark should move 'bout
1 1/4" or so.
I suspect your centrifical advance mechanism is sticky or stuck. Can you turn the rotor at all by hand with the cap off? It should turn ccw a bit and return when released.
The centrifical adv. mechanism needs to be lubricated as part of routine maintenance. At least once a year.
I would use WD40 with the straw on the nozzle and spray through the large hole in the breaker plate. (nozzle tip under the plate about 1/4") Work the rotor back and forth some and follow up with some 20 wt oil or 3 in 1 oil being careful not to get any on the point contacts. You may be able to free it up without taking it apart.