The casting should be useable on most if not all A's, I think. My cabriolet hinges are just slightly thinner than either the ones on my closed cab or the ones on my coupe, and the coupe should be the same as a tudor, and the cabriolet the same as a four door. The raw casting has enough thickness around the hinge pin area to be cut for all of those hinges. I do not know about the open car hinges.
That said, I am not planning to get into the manufacturing business, but if several folks were interested, I could run another batch. I would only supply the raw castings, for the buyer to finish per his or her needs.
The castings need to be undercut (hollowed out) at the hinge, drilled for the hinge pin and mirror head, and threads cut for a set screw. The unfinished casting, once fitted could be simply painted for a commercial vehicle, but additional effort would be needed to shape and polish the piece if it were to be plated. In general, it takes real effort to get a finished mirror like this will eventually be. ...way too much time to do this for anything other than for personal enjoyment. ...way too expensive for someone else to do most of the work for you.
I did this for fun, to see if I could. I have never made anything for casting before. ...but I knew exactly what I wanted the mirror to look like. Each side for the molds was made from five pieces of oak.
It took me about 20 hours time to get the two finished pieces ready for the foundry. I have about the same amount of time in shaping one pair and cutting the hinge area on a second set. Each set gets easier to shape, but doing the reveal 'ball' just above the hinge is a real bear to do, and would not be at all needed for other cars, though I think it will look nice on the cabriolet.
The joy of retirement is I have all the time I want to spend on this sort of thing.
While this is not restoration, the part is an accessory that requires no modification to the car, and I think style-wise, it looks as if it could have been a period unauthorized accessory.