Al: If I read all of the above posts right, NONE of the accepted, available (and cool-looking) mirrors for Speedsters (or Spyders, either, for that matter) will provide really good rear vision without adding some mods, like convex spot mirrors to widen your field of view (always a good thing).
I have Aero mirrors out on the fenders and a small-ish mirror on the windshield strut (it is an old Yamaha motorcycle mirror I had kicking around when I built my car) and I do what IamRay does - set the center mirror and then adjust the fender mirrors to pick up where the center one leaves off and provide some side view. They're not perfect, but they're what I have.
The Spyder mirrors you like, if mounted in the same places as, say, my Aero mirrors, will give the same field of view and would need the same upgrade mods (added convex mirrors ) to be most effective.
Where on the fender you mount them is up to you. Sit in the driver's seat and have someone move it fore and aft on the fender and decide where you most like them. All outside mirrors on the original 356 were dealer installed at the customer's preference so there is no "right" place to put them.