I think the two in the door are for the track extension for the side window. The ones in the upper track of the cab above the door, I think are vent holes. I think Tim had a picture that explained the cab ventilation system. Maybe he will dig it out and post a link to it.
I think you're right Greg,after all the AD cab was marketed as "The cab that breathes".
I thought the holes on the rear edge of the door were for the glasss channel too,although they're in a slightly different location to the earlier pre-51 doors on mine.
