While the frames may be similar for different years and erras of trucks I'd be real hesitant to say "they are the same" for anything except the same body style/year range of the same size truck.
After that use your tape measure and judgement for comparisons.
For example the AD trucks the frame from about the cab forward tapers in narrower at the front, the springs follow this taper, they are not parallel. Later trucks usually have parallel front springs and frame rails.
AD trucks from 3/4 ton to about 2 ton have 36" wide rear frame, later model trucks standardized on 34" wide outside the frame rails.
I'm sure you can do some swapping and fabricating, and it's been done, but not usually as easy as is being made out here.
Grigg
