[MikeK]

The advance curve for a stock B dizzy goes from 600-2600 engine rpm (300-1300 dizzy rpm) and is a progressive straight line add of 7.5 degrees over that range to whatever you set as the initial advance.

Using a "B" front cover will add 9.5 degrees to that, giving you a curve that starts at 9.5 degrees @ 600rpm, then ramps to 17 degrees max @ 2600rpm.

The "B" curve is good under heavy throttle load, but cruising with high manifold vacuum I think it is too retarded for best efficiency, resulting in poor mileage and hotter exhaust. If it also had a vacuum advance it would be perfect!