I think the flat rails look SO MUCH better than the tall SUV-style truck rails, but the tall ones are more useful. Buick switched to the "truck rails" for 1994, and the 95-96 had them as well. Only the 91-93 Custom Cruiser (black) and Roadmaster (chrome) used the low-profile single rail.
SO yes, you can add the SUV-style to your Olds, just look for a 94-96 Roadmaster wagon. I swapped to a chrome low-profile rail on my '96 wagon about 9 years ago.
Can't help on the Caprice...don't know if those rails will work...but I "think" the Chevy rail may be wider.
-Mike