[Clyde]

On the 305 initial timing is set at 7.5 degrees, the vacuum advance has a total of 18 degrees, starts to move at 5-7 inches of vacuum and achieves full advance at 12.25 - 13.5 inches. The centrifugal advance has a total of 30 degrees, 0-2 degrees at 800 rpm's, 11 degrees at 2000 rpm's and 30 at 3400 rpm's thus giving a potential of 55.5 degrees under full vacuum and an rpm of over 3400. On the 351 centrifugal advance is 26 degrees vacuum advance is 18 degrees and 5 degrees initial for a total of 49 degrees at 3500 rpm's. Hope this clears up any confusion, this is from the factory GMC shop manual.