C15 has a 101inch wheel base where as the C30S has a 134inch wheel base.
Long wheel base are 158inch
There are three original Factory photos of this type of tanker but with the earlier 11 cab and not the cab 12 or 13.
The photos are all of the one vehicle.
from the Factory CD by Service Publications
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these are the ONLY 3 photos I have seen of this type of Tanker on a short wheel base CMP chassis in over 35 years of looking