Class A's Ford are usually on the F-53 chassis. Class C's are on the E350 or E450.
The shorter F53 Class A's are usually on a 18K LB's chassis. And then as you go up in length, and or quality, the chassis ratings go up to a high as 26K LB's.
One tip besides rating, is to factor the chassis wheel base length, in relation to coach length. Many of the entry level Class A's are on shorter wheel base's - which result in quite bit of tail hangover. Tail hangover can impact drivability, and dragging onto the ground at places... The term Tail Wagging the Dawg comes to mind, in heavier winds, as as Semi's blow by on the Interstates...
Best of luck on your search,
Smitty