You`re right in the transistion years of the bolt circle with what you`re working with. Chances are your 73 has the large bolt pattern and the 71-72 wheels are the small pattern. Mopar A-bodies had the small bolt pattern (4") up to 72 and then changed to the large pattern (4.5") in 73 but I believe some of the slant six cars still had the small pattern in years after 72. Like the guys said, the first thing to do is measure your pattern and go from there.