While the original HR2 inlet was never really "RAM" air because of the way the alternate air source selector was made. If you had the selector on outside air, the gate was parallel to the sidewalls and allowed any excess air that the engine was not pulling in, to bleed out the side that was attached to the alternate air ducting. Any excess was just blowing into the side of the cowling.
F-1 Rockets had a scoop with an air filter and you can buy the inlet that needs to be mated to your cowling with their filter.
You can also use something in between and is a nice product that Rod Bowers makes that is true "RAM" air and has sprung flaps that in the event of blockage, the suction of the engine will pull them open. The RAM air pushes them closed and all the forward motion of the airplane plus the prop pulses are compressed into this induction. I know folks that have this and get 1.5 inches increase over stock at cruise.
I like the looks of the Rocket myself so you could remake the Y inlet to have two gates with two control cables that would have to be used when using alternate air. The 2nd gate would fully close off the alternate air throat and then all the "RAM" air would go into the engine. http://www.ramairforhomebuilts.com/products.html