So I received the screws & gaskets from the nice folks at Classic Chevy... (I'm not the kind of jerk to call and snivel about slight oversights)...but truth-be-known, I really suck at bodywork, and besides, I ended up drinking breakfast, so I'm not about to try patching up the remnants left on the doors from the previous mirrors, nor am I stupid enough to drive this classic Chevy on the public roads in my current condition...
This really is a great forum for enthusiasts of these terrific trucks!
I get back to you with what I hope will be a job I'm satisfied with.