I am new to the GMC medium duty truck world, but I think my 65 has the standard cab for the 5000 model trucks. I am sure it is not a cab-over and am not familiar with the B-models. Inside, it is much like a GMC pickup cab of the same period (and, in fact, looks like an oversized pickup cab), and there is a distinct front hood that is hinged at the center with the cowling lifted from both sides to expose the 351C V6 engine (which looks very small in such a large space) behind a large radiator. If needed, I could try to figure out how to include a picture.
JRMunn
