Your Body serial number plate looks real to me with the correct fasteners and having the Plant/Series/Month stamped larger than the unit number.
My Parts Books (1951 and 1959) shows "AN" as "1941, 134-1/2", Commercial 1-ton Truck".
"SPECIAL" could mean the GVW on a particular series was either increased or decreased. In your case the 3/4 ton Series "AL" or "AM" was basically increased to be a 1-ton and designated "AN". My parts books also don't show any 3/4-ton trucks having the 134-1/2" wheelbase, they were all 125".
To me it looks like you have a match made in heaven...both the engine and body numbers look right for a 1941 1-ton.
Mike B
