yeah. inside the cowl (at least on my truck) there is, as i recall, a reference for the mounting location for the mirror arm base nuts and washers.
when i added the right hand mirror 4 or 5 years ago, i too was amazed that the kit didn't include a template for locating the holes from the outside (some sort of reference based on horizontal/vertical dimensions). i even asked the counter person if it came with a template and they said it didn't but you could mount it wherever you wanted...? o.k.?!?
after crawling under the dash and removing the vent/kick panel, i could see the two points where the bolts should come through. it seems like such a simple thing to include in a r.h. mirror kit but i guess they just expect everyone to figure it out on their own.
as i stated previously, i would highly recommend going with the parabolic mirror vs. the flat. it really gives you a clearer image of what is on "the dark side" of the truck, and looks pretty original (something i know you have a keen interest in maintaining).
