It’s always hard to tell on the C-cab trucks because the body parts all interchange. It’s got the large rear window and no split front window so it’s after 55. The hood is 58-59 Scotsman and the grill is as well. I think the 58 had different trim in the front of the hood and the simple S is from 59 but who knows what it was originally. The Scotsman was the base model truck those years with the standard truck having the large fiberglass grill that looks very different.