Pinging B$@&%@rd 440!

An O2 sensor might be helpful. Weld a bung in each side so you can move the sensor to check both sides. The sensor is a good tuning aid and can be moved to other vehicles if necessary.
You could take the car to a chassis dyno to have the air fuel ratio checked where the problem occurs. If you do go to a chassis dyno shop have some options available to alter the air fuel ratio or the timing. A sharp dyno tuner might recognize the problem and have a solution.