I thought I would contribute to this thread seeing as this visor topic is very universal. Seeing the images posted by Summiteer above, it appears that the later model 80's visor mount may be slightly different than the earlier models (mine is a 1993) as you'll see.
A junkyard search yielded a promising set of dual visors from a 1994 Chrysler New Yorker. The mount position widths are the same and the color is a near perfect match, however I had to get creative when it came to actually bolting them up as the mount holes are 180 degrees apart and the spring post is too wide for the 80 hole.
I ended up having to drill new holes for each mounting point, but the end result is working so far. Only time will tell if they will hold up, but I like them so much that I would be happy to make a custom spacer to improve their mounting situation if necessary, but for now, they're working great and I would highly recommend them!
Another note: I found several sets of the proper year Mustang visors referenced above and was planning to go that route, but I was dissatisfied with the lack of decent color match and the loss of coverage as you can see in the image below with the black (mustang) and grey (80) visors.
There's also a visor I found from 1992 Nissan Quest that looked very promising, but I never tried it. You can see it compared to the 80 visor in the image below, which shows the 80 visor with a similarly, but darker colored, standard visor on top of it. I suspect the spring post on this visor may not work with the 80 post hole, but it may be worth a shot for those still seeking a solution.
