Retard the distributor one tooth. This will now dictate that you must turn the distributor body counter-clockwise to regain the lost degrees. This should place your vacuum diaphragm between the two manifold bolts.
Thank you for letting me join. The pickup has been in the family since 1954. This is the 5th and last engine. Jack Gibbs built the 1965 409/491 truck short block and assembled the bare Edelbrock heads.