Need part # for vac advance unit

This is for a 1967 273 Commando with the iron dual point distributor, Prestolite IBS-4013A. The vac advance I have on it now is obviously parts-store generic, probably from a later 318 single point distributor. I figure I need to find an NOS advance unit, at this point, but I need a part number to search for. Thanks in advance for any help.