Australian CMP Tipper Question

[cliff]

I have seen two types of tipper in Australian service. This is about the all steel tipper body as fitted to the 60S models.

One has dual rear wheels with commercial type rims the other has the single combat type rim with 18in tyres fitted.

Now are these the same with the only difference being the wheel setup or is it a difference between Ford & Chev models? or is it a different reason altogeather?

Pictured is the type rear body I mean courtesy of the AWM Data Banks. This also shows the single rear wheels.

cheers
Cliff