The only part that stands out is the special order number portion of the DSO. It could mean any number of non-standard options, or just a regular order with specific options, usually paint. The first six Fords I owned were all special order for what I wanted. As this is a 65 Mustang, there is no "Marti Report" available (67 and up) and without a window sticker, it would be impossible to figure out what. Sometimes a factory build sheet gets "tucked" in somewhere.
Jim