My pictures here aren't that good. The top one shows the factory mirrors on a genuine Fairlady Z. The bottom picture is my Fairlady Z with missing mirrors but you can see the rust spot on the fender where the mirrors mounted. There are two large round holes in each fender for the mirrors to mount on. I have never had mirrors with my car so I'm not sure what the mounting looks like.

I could go take a better close-up of the fender to give you a better idea of the location. They basically mount slightly forward above the wheels.