Takkotime: I hate to call BS on your description of how early 454SS trucks were optioned:
My SS is a pretty early 1990 truck (November or December 1989 IIRC with a very low VIN#) and it has the sport mirrors. I bought my truck Feb 14 1991 (21 years ago this past Tuesday) with 4300 miles on it and know for fact nothing was changed on it (bought on MSO from a dealer - never titled). I have always stayed close to the 454SS trucks and GMT400 trucks in general. I have worked on a ton of them over the years and regularly visit salvage yards. My SS has been down to a bare frame and I completely restored a 1990 K1500 ECLB. I also owned a GMC Typhoon for a short time and you'd be surprised how many people seem to have bad info on the SyTy's of 1991-1993. It was a 'dream' truck for me to own when they were new, but I already had my SS. 10 years later I finally had the chance to own a virgin 1992 Ty in immaculate condition. I'm very glad I never sold my SS to get one. Asisde from how quick they are, they really are a POS compared to the GMT400 platform. Sorry to get off track.
All US 454SS trucks had Sport Mirrors as standard. I cannot speak for the Canadian versions -- never really cared that much to discover the differences. The lesser 'sport' trucks did not come with the Sport mirrors standard. All 454SS trucks had 110mph speedo (without tach in 1990), rear sliding window, cargo light, sport mirrors, AM/FM/Cassette w/equalizer, PW, PL, PS w/tilt, A/C, Buckets/console (specific 454SS seats in 1990 & 1991), and various other 'options' that had to be ordered on lesser trucks. The only option on a 454SS was a locking gas cap. In 1990/1991 Black Onyx with a Dk Carmine interior was the only color choice. IIRC 1992 was available in red or white, but only 1993 was available with a different color interior. I have seen tan, blue, & grey interiors in 454SS trucks over the years. Obviously there was special suspension, wheels, trans, engine, dual exhaust (1991-1993), 14 bolt rear end, etc, etc, but most here know all that.
The sport mirrors also came on a base truck (before the W/T designation was available). I have seen many 1988/1989 trucks with rubber floor mats, vinyl seats, no A/C, AM radio and they also had the 5 spoke wheels (6 inch) and sport mirrors. Most of the ones I have seen were either tan or brown (although have seen blue & maroon) too and were 8ft bed 2wd trucks.
A real SS can be determined by an N in the 8th position (454) and a VIN that starts XGCDC14, whereas X= country of production 1=US. I believe all 454SS trucks were manufactured in the Ft Wayne plant (not certain on Export trucks, so there could be a 2 if Canadian Built. To decipher a GM VIN code it is pretty simple and every 'real' US 454SS should have the first 11 digits: 1GCDC14NxxZ (the 9th digit is a check digit and can be different from truck to truck). The 10th digit will change for each year (mine is L for 1990). The 11th digit is Z for Ft Wayne.
Again, I do not know how Canadian trucks were delivered, so there could be some variance. Obviously the speedo will be different.
It's funny how the info on these trucks get skewed over the years. Imagine how skewed the info is on the musclecars after all these years. For instance, I see tons of people on the Pontiac forums state 'how it was' on these old GTO's, when they are constantly proven wrong by people who have original, unrestored cars that are very well documented.
Me - I build mine how I want and don't really care what people think (and I hope everybody else feels the same).