Jeff,
I think the 70/71 set up is the same. If so, sounds like your vacuum retard is not operating as the advance at that rpm is too high. If operating properly, the retard effectively keeps the advance at 0-5 btdc at 1500 rpm but is cut-off above 2200-2400 rpm. Once the retard goes away, the centrifugal advance kicks in to allow full advance to about 30 btdc. Your retard is "going away too early" which is allowing too much advance. Most likely, you have no retard at all.
I would check your RPM relay (one of the two relays on the driver's side mounted toward the front of the car near the battery that look almost identical). Your 2 way valve may also be bad, or perhaps the vacuum lines to the 2 way valve has been reversed.
Best,
Tom Sargeant