Don - Here's a snapshot below of a 1958-59 Serial Number information list from a Canadian GMC resource posted here at
Old GMC Trucks.
There is also a link in that page to an earlier 1948 Model Reference that indicates some "9400" model numbers were rated at 1-1/2 ton (later GMC data refers to truck ratings by actual GVW weights and not by a 1-1/2 or 2 ton classes). GMC Parts Books encourage owners to identify their truck by specific serial numbers when trying to order/identify parts, as there are often changes or differences in parts that correspond to when the trucks were built.
I think to help you out best, it would be great if you could post pictures of the truck and its actual serial number plate (or specific full detailed numbers/letters). This way we can try our best to point you in the right direction for what you need.
