The finned 9" drums were mid-'70 thru '73.
Anti-squeak noise dampers. P/N 2266 298 (for 9" drums), standard equipment starting in '62 and running through '70 -- there's no groove for the noise damper on the finned '70-'73 drum.
Flared-rim 10" drum, rear only, for improved water exclusion and heat rejection. Don't recall what year that started on the A-body, possibly '70—can check next time I'm near my ESF collection.
I am pretty sure A-bodies never got finned rear drums.
OK: How'm I going to find a good American-made DW1057 windshield for my '91 Spirit?! Everything's gone Chinese, and even if I manage to get one without optical distortion, it's a safe bet the Chinese auto glass makers cheat and lie on their safety standards compliance "certifications" just like they do with headlamps, brakes, tires, etc. (PM me if you can help; I don't wanna severely hijack Ulf's thread)