[thefraze_1020]

The SPID is the "Service Parts Identification" sheet. It lists your truck's VIN, wheelbase, and then a list of all of the options your truck received from the factory.

I've seen reports from various owners of 73-87 trucks that their SPID's are located in one of two places:

A sticker inside the glovebox door.
A sticker on the driver's side inner fender in the engine bay.

For example, my 1984 has it's SPID on the driver's side inner fender.

If you find it, look at the list of options, and they will have codes with letters and numbers. These are RPO (Regular Production Option) codes. It is possible to find a list of each of these codes online, as they apply to your truck.