Come on, so when you hit the gas, and need spark advance it will retard? Does the vacuum advance work smoothly or is the distributor a pile of rust?
EGR certainly cannot be overlooked, in these earlier models, no sensors were used, just a thermal switch and again to the venture vacuum to crack it open at about 1700-1900 engine RPM. While the EPA states its to reduce NOx's emissions. It does, its prime purpose is to reduce combustion chamber temperature. Unleaded gas burns at around 500-700 degrees hotter than leaded gas did. First sign of a failed EGR system is burnt out exhaust valves.
Did you ever do a compression check on this thing? Always the first step.
Slightly off topic, aviation never did use leaded gas, low RPM high torque engines, for the high performance engines, water injection was employed. Considered too difficult for the average car driver, so was blessed with the EGR valve. It does effectively reduce the CID displacement of our engines by about 30%. Some playing around with using ceramics for key engine components, but that never got off the ground. Earlier exhaust valve closing is far more reliable, but also more expensive for a consumer grade vehicle. Our vehicles are consumer grade, by the way.
If everything is right, this engine will run fine, question is, what is the problem? Again would start off with a compression check, also like to use a real accurate oil pressure gauge, just to know the engine is okay.