I got the steel from my SO's father, who worked for General Dynamics Space Systems Division for many years. Its T3 something tungsten alloy something alien something something. I think if the rest of the truck was put in a smelter at just hot enough to melt everything to liquid, that steel piece will basically be floating on top and kindof warm.
I had a mirror which came with the truck in a box of parts, so I sanded, refinished it, but was missing some of the mounting hardware. All I had was the top retaining plate with the cup in it, but nothing else. The mirror has a solid arm mounted on the back with a ball on top.
I drew up this highly accurate schematic
Basically, a yoke which would fit underneath the ball on the mirror arm, held in place from above by the plate and some fasteners.
The one thing I did not have in that drawing was the rubber grommet I popper over the round ball on the mirror arm so I could use compression to hold the mirror in place. You can see the edge of the rubber grommet and the way the steel yoke comes together under it, the mounting screws pulling it all together.
Thats not rust in there yet, that's "character" still. Not much of a view afforded by the rear window, but it's something I felt it should have. It works perfectly, and the rubber grommet holds it well in whatever position with no noticeable vibration when driving.
