Not a great engine, compared to the similarly sized 270 in the GMC.
There are a few parts that were unique to the Chev, such as running boards, engine side panels, floor panel, and I think some slight firewall stuff, otherwise much the same as GMC.
From memory Chevrolet made one largish batch of panel vans, the majority of which went to a specialist sub-contractor to get turned into signal corps trucks, leaving the un-modified panel vans as much rarer than the signals units.
If you see it again have a look for the spare wheel mount bolted to the side of the chassis behind the drivers door. A panel van came with a full cast steel spare wheel mount. Conversions to signals van usually involved torching them off level with the running board to make way for the side equipment boxes. If your find has a stub of a spare wheel mount, or marks where one was torched, then it is probably the K-51 signals van.