For the T-Tops, the bracket base is flat....three screws. For the hardtop, the bracket base is raised, rounded on top, if you will, not flat, three screws.
The lighted mirror bracket is 6 inches long.
I'm not sure, but most of the Grand Nationals came with a mirror on the passenger side.No lights.......my '87 did, but I switched the passenger side to a lighted flip up mirror visor, with the bracket that had a hollow passage in it for the power wire that runs up into the roof material.
Hopefully, someone else will chime in on the availability of mirrors on the GN.