What changed in 73?

Lots and lots and lots of things changed. First year for big bolt pattern wheels on disk brake cars. First year for reinforced impact bumpers. "I guess?" first year for heavier reinforced doors. As stated but more: The K member was different. Not only did the motor mount perches go from pillow mounts to spool mounts, and the steering linkage is different, but the anti say bar goes INSIDE the K member, and the connecting tabs for them on the lower control arms are different.

You would have to check the fuel tank. There were changes allmost every year in the evap emission control system. The earlier years used a big vapor separator in the tank. Later years incorporated the separator right in the tank, eliminating several external tank fittings and plumbing.