"3" series part numbers started with the 1970 decade vehicles. "2" series part numbers were 1960 decade vehicles. "1" series part numbers were 1950 decade vehicles. Chrysler's general rule, but a "2" series part number (for example) could be used well into the 1980s, if the part didn't change numbers later on. Seems like some of the '66 Imperial cars still had some chassis part numbers that dated back to the later 1950s, when that torsion bar/leaf spring chassis was put into production?
I have seen some "29_____" numbers used for the first time on 1970 models, though. Then it seems that things started to be modified a bit in the 1980s?
Just some observations,
CBODY67