../... my left mirror doesnt appear to be either the "early" or "late" that I see advertised everywhere.../..
Like is already pointed out to you here, the mirror face does look like the correct M-B type - stem is not. However, I think your present mirror stem looks quite ok, and your idea of leaving it there sounds reasonable. Perhaps just treat it a a peculiarity, making it just your own car
If you remove it, as you mention, you will need to fill the holes now in the door skin. If you fill by means of welding, you will need to repaint the door - not trivial as you have a metallic paint. Cover buttons is the other alternative...
Cars didn't come standard with outer rear view mirrors. Probably yours had none from factory, and the dealer or an early owner fitted the mirror we see there now
/Hans in Sweden