Gm C body interchangeable?

Read somewhere that GM C bodies and D bodies share alot of the same parts as the 77-96 B bodies, with the exception of the frames being wider and/or longer but the trailing arms or some the of the suspension components are the same or interchangeable.
An acquaintance of mine has a 76 Caddy Seville/ Deville 4 door and wanted to.know if the current 77-96 B body aftermarket trailing arms will work , or the 70 -76 ones will.
Thanks

77-96 is the wrong B body . The 71-76 Caprice & Impalas are also B body also but they are quite different from the 77-96, the 71-76 have much

larger  bodies and frames. The later B body 77-96 is based on the old mid-sized A body frame from 60s and early 70s (Think GTO)

So the Cadillacs you mention have more in common with the older B Caprice and Impalas (71-76) than the later B bodies (77-96).

The only Cadillac sharing parts with 77-96 is the D body Fleetwood made in late 80s and early 90s.