The 10,000 day calendar used during the muscle car era started on July 29, 1961 and ended on December 13, 1988.

The calendar starting date would appear on the part as 0001 and ending date would appear as 9999 (or maybe 10000?). The decoder below can be used for that calendar.

http://www.lightningjar.com/decoders/10k_day_calendar/