Out of the Shadows
If you open your driver door, there should be a silver and black sticker that has the VIN number along with vehicle weight data. The top right corner will have the month - year the car was produced (5-75 would be May 1975). Bottom left corner of that sticker has a MDH with numbers below indicating the month, day and hour car was produced to really narrow it down. If yours is a late build it would be July or August (very late) 1975.