If you're interested, I have a cold air intake that would fit your truck. I snagged it off a mid-80's D250 at the pick-n-pull for another project, but it didn't fit well for that deal so it's just lying around at the moment. You can have it for the price of shipping if you want it. It mounts to the driver's inner fender and goes behind the battery tray to the radiator support. Here are some photos of how I installed the same thing on my 82 D150. The duct has some kind of port at about the half way point but I just plugged that on mine. I scrounged the same junkyard for a generic flex air hose to go from the round exit to the square intake on the air cleaner. Shoot me a PM if interested.
Here's the part:
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I pulled the battery tray and cut a hole just under the turn signal for the inlet.
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The final version. It's clean and works well.
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