I'm guessing that pulling air from the radiator inlet will work, but you'll definitely want a blower to move the air. I don't think you'll get much ram-air effect there since most of the ram air coming in the big nose opening will be going through the radiator.

I used the brake duct opening to pull air to my driver side footbox. Go faster than ~25 mph and I get good flow just from the ram air. When I'm stopped or moving slowly, I turn on the blower. My entire system (including butterfly valve) is home made. For the fan, I use a bilge fan blower purchased at a boating store. It works great.

I agree with David H. You need to block off all the areas between the footbox and the body so you don't get engine compartment air sneaking into the cockpit.

David