John, first off welcome to the forum!
Thanks for the story and pictures of your SSP Mustang. I love it when a car turns up like yours and the Buck Tags clearly show the agency and SSP option. There are not many R.C.M.P. SSPs out there. I added your car's pictures to our VIN Project,
as seen here 
I recommend that you look into buying a Marti Report...
https://www.martiauto.com/reports2.cfm
...which will list the options for your car and determine the DSO number (unless you can read it clearly on the Buck Tag). You can also buy a replacement door VIN sticker for your car from Marti.
It's pretty cool that the replacement door on your car
may have come from a SSP (based upon its 6-digit DSO). That car is the last of 3 consecutive VINs. I will add that VIN from your door to our list of cars where we want to run Marti Reports to determine if the donor car was a SSP.