The shape of a 1/2 ton AD frame compared to a 3/4 is much different.
The 1/2 ton is narrow at the front and wider at the back, tapering the whole way. The 3/4 ton only tapers from front to about the middle of the cab, from there back the rails are parallel.
I'd say that a 3/4 ton is a lot different than a 1/2 ton when considering frame, axles, brakes, and suspension.
Yes the sheet metal is the same other than bed and running board lengths.
Grigg