I believe the seat belts varied between the '73 and '74 models. '73's used a pin on the seat belt receiver while the '74's used the standard receiver to lock the shoulder belt. (I don't really know because I'm still missing my front seat belts.) The easiest, but not always the best way to tell is that 340's were only offered up to '73, so the '74's biggest engine option could be the 360 they introduced for the E-bodies that year. The best way to tell is the bumper filler guards were used on '73-'74's, '72's were tucked closer to the body like the '70-'71 models, '72s used chrome bumperettes while '73-'74's used the larger bumper guards w/extra rubber and had a metal back plate behind the bumpers.
