On your door tag, directly above "DSO" is a six digit number.

It is 740023, same as the other car already in the VIN Project.

74 = Seattle (WA) district sales office
0023 = domestic special order #0023 (for the 1988 model year)

Mustangs with six-digit DSOs are usually, but not always, SSPs.

I'm gonna say WSP. Ordered In Washington, white with blue interior, single and spotlight. The two holes at the top of the dash in the center might have been for their switch box that was mounted in that spot on the dash.
OSP wouldn't be ordering their cars out of Washington.

Gotcha, had to clean the glasses to see the little dso. Yes it is the same.

What would really help ID'ing the original agency that ordered this car (and possibly every other VIN in that same batch) would be the buck tags...

http://www.specialservicemustang.net/Bucktags.html

It sure looks like my buck tags are gone. It seems like I can see where they were, with a little hole where they were attached, behind the drivers light.

You did look down lower than the upper bar on the radiator core support, right? When Dearborn went back to stapling them (mid '88?) they moved them back down lower where the very early ('79-'80?) Fox tags were.

Yes, that's where I looked. The area I suspected them being appears to be the marked area for the 88 up.

OSP cars have been verified with the DSO 74 ordering district on them.

OSPs were ordered through DSO 74 (Seattle) but all of the Marti reports that I have seen show them being sold through Damerow Beaverton Ford (dealer # 74C017) in Beaverton, OR.

Hmm. Never knew that. Interesting thing learned today.