Might also add every GM car shared the same body from October 1957 up. This was GM's better idea of having people pay Cadillac prices for a Chevy Impala. The only difference prior to 1973 was the motor under the hood was unique to the marquee Everybody had their own motor which differed from every one else's motor). After 1973 just about every car had a Chevy SBC V8 under the hood or a Buick V6.
The other big difference in the price point of the car was the standard trim level. As the car base price rose the number of standard trim and luxury items quality improved (Chevy had a wood grain vinyl trim dash decal, a Cadillac had real wood veneer that looked just like it). You could order all of the options that appeared upon a Cadillac in a Chevy but, it drove the price up higher if you tried to buy those parts on a Chevy instead of just buying a Caddy because you wanted that 283 cube Chevy motor rather than the 500 cube offered by Caddy in the same car body. (it was a OHV 331 Caddy engine that was sung about in the song "Hot Rod Lincoln" replacing the original 239 cube Mercury Flat Head to make those telephone poles look like a picket fence).
So that over stuffed pillow top Cadillac glove leather four way power seat will bolt right into your Impala. Or the powered split bench seat in crushed velour out of a Buick. Maybe you want a set of Sporty Buckets with a center console out of a Pontiac Parisian or a Bonneville 2+2 (same B-body car). Only the added two feet of interior room behind the driver's seat in a Cadillac Limo makes the car different in terms of the sheet metal and parts interchanging (Limo was a D-body), but the seats still fit.