used a standard early 70's air cleaner, had some cheap thin metal shelving left over, used one shelf each for the ducts. drivers side pretty simple jst used a roller and welded it up. pass side hade to put a bend in it to clear the a/c hoses.
It is tempting to run ducts to the cowl since the area at the base of the windshield is a high pressure area. I tried this 45 years ago on my 68 Roadrunner after reading a magzine article. What I didn't think about was the cabin air conditioner/heater also draws air from the cowl. Came out the next day and gasoline vapors were on the inside of the windshield.
So if you take air from the cowl, you have to completely block off the vents to the a/c heater
Have had no issues from vapor's other than when I plumbed in the valve cover breather in to it. removed breather and ran it out side of air cleaner no more issues. also with breather hooked up to air cleaner, at speed, started to have valve cover leaks. who would of thought you would get that much ram air through the vent hose to the breather