Harvester said "Also, I would not run the engine at 2000 RPM as suggested previously, because ported vacuum (distributor vacuum) will be applied to the vacuum advance at that throttle position..."
On an old Rochester model "B" there aint no above throttle butterfly vacuum port or "spark port". The distributor gets its vacuum from a port BELOW the throttle butterfly--thus it is getting full "manifold vacuum" at all times. This "ported spark advance" system was not around on Chevys prior to 1968, the first year of smog era carbs (thus no mo' model "B"s around either).
