Alright gents what you have all been waiting for!
I went around the edge and went slow and tack welded the corners and a few more in between. I didn't up the paint really at all. The mirror overhang covers most of that and then the weatherstrip or windshield sealant I use to seal it up tight will let you see none of that.
Inside view with mirror mounted
Instead of doing it how people do it and weld the entire edge and have to do body work/paint of the plate I did one step further. I traced a cardboard template the exact size of the mirror, painted it black. and then took my grinder until the plate fit slightly inside the mirror base, so I would have a bit of an over hang of the mirror itself. I also took a file carefully to a couple edges of the mirror itself so it fit flush. With my plate size it fits the mirror exactly and I do not need to mess around with painting like those guys do when they have several inches of plate showing. You can not see any portion of my plate.
I then marked my large stud hole (when you get mirrors you will see one of the holes is longer. Once I had that I then marked the other 3 holes, for the mounting bolts from plate to mirror. I put that at the front of the vent window (just gotta kind of eyeball it), and then marked 4 locations for self tapping sheetmetal screws (I used a diamond pattern and they hit solid meat). My location is also in a recess inside the mirror itself so it doesn't effect mounting. I then weld around the outside of the plate with my mig and tacked it on the upper and lower corners and just about anywhere else I felt necessary. I then tacked my screw heads so they wouldn't back out. Pulled the vent window back so I could access my plate, and was able to get 2 bolts into the mirror. Refix vent/door panel.
I am going around the outside of my mirror where you see that .25 gap or so, with black butyl windshield sealant, or weatherstrip to make all that look factory and protect it from rust where I hit with the welds. I plan to touch up the paint a bit, but if you are careful with the mig and keep the heat low you will not mess up your paint too bad.
I would highly recommend that you use a mig, or at the least a wire feed. My two pieces of advice, keep the temp low, and wire feed accordingly. I used the chart on the door, which called for like 90 amp, and 120 wire speed. I ended up using 100 wire speed and like 80 amps. It seemed to do the trick. I wanted to avoid blowouts, and warping the metal, or burning the paint off farther than what my seal would cover.