Speaking on the 322, what color is yours painted? Mine is Chevy Orange, but most sources list them as being Red. Can you add some engine pictures to your webshot page?
I don't have any literature on the big 10-lug axles being offered in 1957, but I do see a part number for the wheels in my 1963 parts book starting in 1957.
Fire trucks were always built different. My brother is the President of a small VFD and they just bought a single axle tanker with a 52K gvw, so anything is possible.