Welcome to the Team James and Mrs.!
I do not believe the 1973 is unique; it just isn't as popular as the 1958-'64 X-frame cars, or the second most popular 1965-'70 body styles that had a 427 BBC and disc brakes from the factory. Your body style was shared with the 1971-'76 production years.
In that band all of the car's parts should interchange. You need not restrict your self to just Chevys though, as after 1972 you needed to read the trim to know who is selling you the car because Chevy, Pontiac, Oldsmobile, Buick, and Cadillac all shred parts including motors. A Cadillac was just an over priced Impala which is why the Olds and Pontiac line disappeared (people finally figured it out and sales dropped, with Buick making the cut only because the Chinese people love the American made Buick).
In the case of seats everybody except the entry level on price point Chevy cars had a split bench seat with a middle arm rest as an option (standard on Buick and Cadillac). And following marketing rules set down by GM; though the seats were identical, the fabric covering the seats could reflect the branding and luxury level (crushed velour on Buick seats and leather covering a Caddy seat).