i have the passenger side mirror arm from grumpy's
http://www.grumpystruckparts.com/ as mentioned by bowtietim, you do look through the passenger windshield to view traffic in that mirror. i've put a parabolic mirror (napa carried it and it looks exactly like the original stock mirror) and it really helps "see" the traffic on that side of the truck. if you are going for originality, use the flat mirror.
as far as i know, all the original passenger mirrors were viewed through the windshield, not the door window.
