I think that 1989 was the first EFI (TBI) Ford Class C, so a "1989 RV" as designated by the coach builder might not have been on a 1989 chassis. If specific feature changes are importatnt to you, check for the Chassis Year as well as Coach Model Year.
The coaches in your two ads are quite a little different. The one on Chevy does not have "bed down" like the one on Ford does. Floorplan (including bed arrangement) is really important. Making sure it doesn't have water leaks or water damage is really important.
If an ad says New Tires, verify. There are date codes on the sidewalls.
The 460 Ford has the power to go anywhere except extreme altitude, which is a limitation of carburetors, not Fords. The 350 Chevy would have OK power, a little short for western mountains.