help with replacing rear view mirror, please

I want to install an aftermarket interior rear view mirror. I was thinking at first just for the map lights, but now that I see what's on the market, I will prob go for the auto-dimming, compass and outside temp features.

I have my rear view mirror in my hand. Took off the cover, removed three screws. The "stalk" of the rear view mirror is still attached to the mounting plate by what looks like a hollow SQUARE set screw, so I cannot separate the mirror from the mounting plate because I don't have that kind of tool. I guess I need to go out and buy a set of square (?)screw drivers. My Allen wrenches won't fit.

Anyone have any experience in this? Do I reuse the old mounting plate? Any certain type of mounting hardware I need to order with the new mirror? Has anyone used a certain brand or model of mirror they like? Any help appreciated.

 

The squares are pretty common, if you can I would reuse the (already glued) mount, should be standard.

 

The mount is not glued on. The mount is screwed into the sheet metal of the roof and covered with a plastic trim garnish. I am aware of the standard glued on wedge mount buttons and the cam lock mounts for rear view mirrors. My truck has neither.

What I will prob end up doing is removing the stock mirror entirely. I still need to figure out how to separate the mirror from the stalk. Looks like I need a Torx driver or square screw driver for that. Then I will put the plastic garnish back without the mirror, and use a glue on wedge mount button directly on the windshield for the aftermarket mirror. Clear as mud?

 

Clear as mud !