Sounds to me like it might be lean, or it might be the vacuum pod adjustment. There is no reason to unplug the vacuum advance on this car except ignorance... So lets fix that. The vacuum advance only works at light throttle and cruise conditions. It add advance to the engine at these times because it gets much better milage and more power with less throttle. But, it's "tuned" for a certain level of vacuum. The cam change affected that. So now you need to adjust it. I believe what is happening is the timing is getting advanced too much at cruise. There should be a small allen wrend that will just fit inside the vacuum hose nipple on the vacuum advance dashpot on the distributor. Something like 11/32. In any event, unplug the hose, take that allen wrench and stick it into the nipple... It will go in and engage a screw in there. Turning clockwise will lower the vacuum required to advance. Counterclockwise will raise it. I go two full turns as one adjustment. Drive the car with the hose connected, disconnect and go two turns counterclockwise, reconnect and drive agin. When the surge is gone it's done. No reason to lose it entirely. Also, you may find that tuning the rest of the ignition curves will help it run better too.