Yes, I know that this has now gotten "off thread", but I hate to leave a "hanging chad", so to speak. While my knowledge of 1969-73 Mustangs is limited at best, I can still read. According to the 1969, 71, 72 and 73 (I don't have access to 1970, but would guess that it would "follow suit"), it appears that the Dual, Color-keyed Sport/Racing mirrors were Standard on Mach I's, Grande's and Boss' of those years, and available as Factory Options on all other Models. As I noted, this is based on what is printed in the Sales Brochures (which would explain where Tony got his information), but if in reality there was something that changed this Option, it would be something specific that I would not know about.
Just thought I'd help provide an explanation of where this information could have come from.
Bob