so are you saying that all the prestolite distributors after 1965 are after market? how does the ISB # and part# and date code end up related to production distributor? I can understand the part # , but the ISB and date code I would Question . What I am trying to determine is which distributor is correct for production line (what was original to the vechile). as I stated earlier there seam to ample supply of both available with similar date codes.