If you have a part number AND a old Chrysler dealer who still has the old paper parts books with the supersedes numbers they can, IF they are willing, search for the most up to date part number for pre 80 something parts.
From there they can do a search of their nationwide system.
This is how I got the last known OEM 67 dart compatible fuel sender in the Chrysler system.
Local dealer said to call a dealer in Denver and they were able to find a supersedes number and found one in the system in a dealership in GA.
having the latest number will greatly increase your chances