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In the late 80s I had an under dash unit in my '68 that would essentially freeze the inside of the cab. It was one of those centralized deals where the whole thing hangs right under the factory HVAC controls and had 4 vents. Pitty the fool that had to sit in the middle
The cooled air doesn't have to waste any time going through ducting before being released into the cab and impacting the occupants!
Back then, I purchased all the necessary parts at salvage, including the under dash unit and all under hood components, had the lines made at my local parts house ( think barbs and clamps ) ...then installed it myself. Don't remember how much but I was broke so it couldn't have been much.
-klb