Thanks for the lock Fabrizio. An afternoon of research has shown me that this is no ordinary Diamond T, and information on the internet regarding it is rather rare. Most of what I have located comes from a single blog, previously unknown to me, so I hope that it turns out to be a reliable source.
According to this source: “This truck is a prototype Diamond T COE (Low Cab Forward – Tilting Cab), built by the Murty Brothers Automotive Equipment Company of Portland, Oregon “ Apparently, sometime in the early 1950's, Diamond T contracted Murty Brothers to design and build (completed about 1954) this prototype, as the Diamond T engineers were busy designing the 921 Series COE. I have been unable to discover a model number specifically assigned to this prototype, however here is a Murty Brothers patent, dated 1956, relating to the design.