Like most early cars the motor sucks hot air from under the hood; it's cold during warm-up (when inducting warm air would improve things) and hot once warmed up (lowering air density).
Short of a hood scoop, the easiest place to suck cold air is through the grille, and to each side of the radiator happens to be a nice flat blank area...
So for a cold air source I chopped a large hole in the passenger side radiator support; luckily it unbolts and can be done off the car. This incidentally weakened the hell out of the support, so I added a simple brace to the inner fender.
I coupled the cold air through the grille and holed support with two sheet steel adapters and air duct hose from NAPA. The adapters I bent up from flat 18 gauge steel stock.
One adapter fills the hole cut in the support, and connects the duct hose. It's angled to point up towards the carb; water and pebbles driven in through the grille won't make the 12" or so total rise; in the last year of use, very little sand has reached the box.
I also killed two birds with one stone: the early American air filter is not common and slightly expensive. The later AMC air filter, CA184, is common as dirt, and I happened to have a decent airbox in the junkpile (never throw anything out!). It had a thermo snorkel which I removed and pitched, and made an adapter out of more sheet steel for the air duct hose. The adapter changes shape, not area, so it ought to flow well. I also plugged the existing crankcase vent hose hole and installed the one off the old American's airbox (not shown here).
The whole thing worked out neat and clean. I painted everything after I took these pictures with Eastwood Chassis Black. It looks like a factory installation, simple, solid, clean and neat. The new airbox doesn't really fit the airbox adapter bolted to the top of the carb; it doesn't sit square. I just unrolled the lip on the airbox to decrease the hole diameter the 1/8" necessary to make a correct fit.
Since it's unpainted here, you can see the new air intake relative position behind the grille. Depending on what I later find in the airbox, I might add a coarse screen to the intake.