Ford Motor Company's SPECIAL EQUIPMENT PARTS LIST was usually provided to the ordering agency and lists the special equipment installed on the vehicles for a specific Dealer Special Order (DSO). These list specifc parts (by number) for the optional equipment installed, such as single-key locksets, wheels and caps, etc. It's pretty rare to find these sheets still with the original vehicle.
Here are several examples: 1983 Colorado State Patrol Parts List, DSO 76-0029. The total number of units ordered (6) for the DSO is listed, as are numerous part numbers.
CSP Parts List envelope.
1985 Florida Highway Patrol Parts List Parts List, DSO 24-0599. 66 total units, and note the 1986 part number for the center caps.
