Knowing you,
mikester , you probably have a stash of Malibu/Monte covers. Or maybe you have a big stash of Olds covers. What do I know? The Chevies won't straight up swap to an Olds. I'm curious as to what may be different on the Chevy vs. Olds filler panels. It appears they're the same by just glancing at the pictures. But closer inspection has the vent hole is cut differently, as well as the length of the rounded part that hugs the bottom of the steering column is longer on the Chevy style.
With A/C-
78-88 Olds Cutlass uses p/n 557370
78-88 Monte Carlo uses p/n 459507
78-81 Malibu uses p/n 459507
82-87 GP uses 547856- no vent. Just a long cover plate.
82-88 Buick Regal p/n 1257352, then 25503014, then 25513679, and finally 25520634. It doesn't look like the others.
Didn't check, but figure the Elky's were the same 459507 if I were betting on it.
They may physically interchange between Chevy and Olds, but what looks different to me is the vent itself. It looks like the Olds version is extended out more than the Chevy version, and is a little different. Olds vent just rolls up and down and it's on when the A/C fan blows, while the Chevy version I'm guessing has a vent control lever or something on it. I'm not sure, but if you had the vent and attachment junk for either, you might can interchange them. But I'm not sure. Never did it. Didn't even research this before today.