Question on CMP 3-Ton Break-down Lorry (Wrecker)

[Grant Bowker]

To my eyes, Chris' hook spring is tucked well inside the frame ends using brackets typical of a (later) GS truck while John and Bob's photos show the spring about inline with the end of the frame rails (or perhaps even a bit further aft?).
Both wrecker bodies do seem to be sitting tight to the frame rails. Perhaps to keep them secure against odd loads and provide clearance under the booms?