I believe the Chrysler Industrials never had a vacuum advance as they were designed for a steady load at rated RPM as used in tractors, combines, etc. Your Chilton manual will be for automotive applications. The timing could be different for the automotive and industrial version and just may be at the root of your problem if set to auto specs.... I'm not sure on this..... I see no reason why an automotive distributor with vacuum advance couldn't be swapped in to replace the origional. Maybe we are on to something here ! Anyone else have ideas on distributor swapping for better performance ?
Clarence