AD Chassis vs. 55 2cd + ?????

[arkracing]

Anybody know what the differances are in the AD '47-'55 1/2 chassis and the '55 2cd + chassis' are?

I looked @ a '52 today, but the guy said the chassis that was under it was from "that truck" and pointed to a '55-'57 cab/nose that was sitting on a later dually chassis.

Just curious as to the differances, the AD cab was just sitting on the chassis, but looked like it fit pretty well over the rails.

Thanks in advance,
Andy