I JUST finished up on a mirror swap on my ol C65 GMC...Doors are exactly the same.... Used a pair of parts yard specials.

$10 a piece. Stainless. Fasteners and all.
They are from a 95 or 96 dually flatbed. The HD's use these too.
You can see the damage on the door where the old mirrors were. Gotta patch that up.
Couple things on getting them to fit, The top two braces will need the ANGLE changed on the door side. As in the tabs need bent upward some. The top REAR brace will need twisted downward slightly too. Of course the bottom brace will need a new set of holes too but they set perfectly on the door. I used a 3/16X1X12 piece of flat steel that is drilled and tapped (metric bolts here) and glued to the inner doorskin just to hold it in place until you draw down on the bolts. You could hang on the mirrors if you wanted to.