My '77 wagon has the STD mirror. I really miss having the prismatic - but can't seam to remember looking for one when the chance arises (sigh).
Unless you can find a broadcast sheet (which are rare) or have the original window sticker, who will know that you have the wrong mirror in your car? It is not something I would look for, even if I was buying, or judging your car in a car show, unless the car was worth $200k or more (which wouldn't be an FMJ in that case...).
Thank you X and Aspen for answering his question.
Buy the way, there is almost nothing that fits an L-body (Omni or Horizon (M/Z)) that fits anything else Chrysler made - except for a few random fasteners. Those cars are so odd-ball even compared to Chrysler's other FWD cars.
BudW