Call 800-222-1020 (GM) and ask for a "restoration packet" for your car. Have your VIN and mailing address ready and then wait anxiously by the mailbox :) (though actually, both of mine came via UPS) Unfortunately, for most of Canada, this service is NOT free... it is free in the US. EST hours are: 8am - 5:30pm M-F
All the car's original options can be determined by the codes listed on the trunk lid sticker. Make sure the VIN on the sticker and the VIN on your car match, as someone could have changed the trunk lid if you are not the original owner.
In '87 when GM cancelled the Buick Grand National, they kept the plant running until December, and all of the GNs built after August were still labeled as '87 models. We who owned them called them '87.5s to distinguish them from the regular '87s. It is interesting to note that Monte Carlo SS's were also built in the Flint plant alongside the GNs, and those built after August were indeed labelled as '88s! It would be possible to have an '87 GN that was actually built later than an '88 Monte Carlo!
The steering unit on SS's is one of the most desirable units on the market as far as G body's go.