wow, that cab looks NICE. is it yours or a pic of a truck like yours?
some of those aftermarket louvres would fit in there if you can find something that looks period correct. personally, I would hide the a/c behind the glove box like the vintage air system. that would keep you happy from all angles most likely. out of sight, nearly. not gonna freeze the 3rd guys knees. heats AND cools in one unit. parts readily available. downside? price. but weigh that against the other options and how long you plan to keep the truck and what that option will increase the truck value should you decide to sell one day.
a few outlet choices. they could be placed in a lower dash valance that you fab to cover the section of the a/c unit that hangs in sight below dash. that way you don't have to cut the dash up.
https://www.summitracing.com/parts/vta-490538
https://www.summitracing.com/parts/vta-492056
https://www.raceplumbing.net/Vintage...h_p_89333.html
http://theairshop.com/louvers/
http://hawkhardware.com/index.php?ma...123_27_209_215
http://www.curtsrodandcustom.com/vin...cessories.html
that should keep you busy, haha.