The fresh air intake for the HVAC system is just below the windshield passenger side. Simpler to just run the pipe through the firewall into the cab. :rolleyes5:
Do stacks the right way in the bed of the truck. Like this local 6.5 example:
I like stacks on trucks that actually work and pull a load, I like the look of a loaded truck rolling coal out the stacks. A race/pulling truck with a hood stack would be ok but a DD would get annoying.