I think your problem is the big valve circle track head, and the fact that your runner velocity is so slow that fuel is falling out of suspension at slow air speeds, causing roughness and poor fuel distribution. Try a head that is not cut up, with standard sized valves, blended bowls, polished chambers, and a three angle valve job blended into the throats.
You wont hurt that powerglide by engaging it at 1100 RPM. If changing the head seems counterproductive then sleep well knowing your trans will live and live with the "problem".
