'84 1/2T Dumbo Mirrors

[Ironhorse]

Friend of mine just recently bought the above truck and is working thru some condition issues to use it for a daily driver. The passenger side dumbo mirror was broken in it's previous ownership. We removed the outside stainless cover which had one Phillips screw holding it. From there were two 10 mm bolts that held the arm mount in place and guess it provides tension. It was apparent after loosening those two bolts that the mirror arm would not slide up and out as there seems to be a collar of some sort at the lower end that is on the mirror arm. Three bolts appear to hold the entire assembly to the door skin of the truck but they are not 10 mm size, maybe 9 mm as they are smaller than the 10mm wrench we had. With the correct size wrench is it just a matter of removing those three bolts and the outside assembly comes off or is there a "backing" plate in the door cavity that will then fall to the floor. Sorry if this is a dumb question but I'm a 67-72 guy and not that familiar with these new fangled modern trucks.