I've never like fender mounted mirrors, so I searched for alternatives and found something similar to the Bugeye part. My 1957 TR3 has the Dzus-style stanchion attachment to the scuttle. I removed the windshield as well as the rearmost Dzus on the driver's side. I then removed the stanchion plate and removed the wire on the back side, which the Dzus fitting would have locked to. Using the stanchion plate as a guide, I drilled a 1/4 inch pilot hole in the inner plate (through the slot in the scuttle), then reamed that hole to 3/4 inch diameter in order to pass through a bolt.
I had previously located a vintage Wingard mirror on eBay (era appropriate), which is threaded at the base for a 5/16 x 24 x 1 bolt. I reattached the stanchion plate to the scuttle and mounted the windshield, locking it in place with the three remaining Dzus-fittings. Feeding the stainless bolt through with washer and lock washer, I place another stainless washer in the empty recess where the Dzus would have been (it fit!), I then placed a thin, rubber washer (which was trimmed to the diameter of the mirror's stem base) over the bolt, and threaded the bolt into the base of the stem. I used a socket driver to tighten the bolt to the stem once the mirror was correctly positioned. I then adjusted the mirror while sitting in the car.
The first photo shows a TR2 where the idea came from, the second and third photos show the installation on my car. It looks like it was a factory-fit.