I like to go by "common to all car" dated items - i.e. parts that every Mopar came with such as voltage regulator, wiper motor, alternator etc. These parts were used on pretty well all cars (B-body for the wiper motor) and such the inventory was freshened pretty regularly. This is assuming the originals are still on the car. Of course you should throw everything else into the mix such as Engine Assy. Date, glass dates, tire dates, wheel dates, Shocks, Dana, VIN and all the other parts discussed in this thread. Compare your findings with other known cars and it should put you in the ballpark.