I'm trying to retrofit some things and see multiple part numbers for what is otherwise the same part. The difference between them is what I'm calling the option code. That's probably the wrong name, so maybe someone can educate me? It's not an RPO code. Anyway, I see CK309, CK310, and CK314. Can anyone tell me what these mean so I can figure out what I need? Looking at parts for a 1998 one ton K3500. Thanks in advance.