These are the two varieties of the 965 Euclid Dump Trucks. The front one is the type with no windows and the rear one has the windows. I just had to replace the tires on one of them. 

Below is a rare version of the truck with the Terex name. It is a new casting as it has Terex cast into the radiator as opposed to Euclid. This toy had a broken dump box hinge but I have repaired it.

I do not know of any other types of this toy although I have found a dump box painted in orange. It looks like original paint, and the dump box is identical to the Euclid. Maybe a promotional toy? Any information would be most appreciated.