I will try squirting some fuel into the carb while revving it a bit under load. I agree no ether for safety reasons and to avoid washing the oil out of the cylinders. I'll keep the fire extinguisher handy in any event ;-)

Advancing or retarding the timing affects power as expected, and idle at the two extremes, but it doesn't seem to have much effect on the underlying difference in behavior under load/no-load conditions.

The only other Mopars I have are two 1965 Coronet 500s so no spare ECUs to try. AutoZone has an ECU for $30, so I may as well just throw parts at it and try a replacement. I'll pick one up tomorrow. The ballast resistor is good.

If those two actions fail, I will pull the intake off and check it for cracks, leaks, or a clogged crossover.

I appreciate all the ideas. This one has humbled me...

Thanks to all,
Bob