The way I do it is I get an air filter that is just short of the hood when its closed and bigger than my hood scoop hole. I then glue a 1/2 inch thick foam rubber strip on top of it. I made a thin hold down out of a small steel rod with a loop bent in the middle and I screw that down to the top of the air filter(no top lid on it). The air filter with the foam seals up against the hood and makes it pretty much a ram air. If I wanted to block it completely I could put a thin metal strip around the air filter but I haven't bothered with that.
The ram air I made was intended to be temporary,as I just wanted to test it.I was looking around the shed and saw an old cookie sheet that my wife had thrown out.I cut a hole out the centre using a gasket as a template and made it to just fit over my carb.This was a good base but was still about 4 inches from my hood.I was going to seal it with foam but I was in the store and saw a tinfoil turkey roasting pan that looked exactly the right shape and height.I took it home and cut the same round hole in the bottom to go over the carb and set it on top of the cookie sheet so it would have some support as the tinfoil was very flimsy.I made the holes in these two pieces just big enough that my little 10 inch air filter base fit down throught it and on the carb.The whole thing is sandwiched between the float bowls on the bottom and then the air cleaner sitting on top of it and held on like normal with a wing nut.The turkey pan seals all around the air filter up to the hood and the filter is stuck up right into the opening of the scoop.I hope you can make some sense of this as it is hard to explain but in the end it only cost about 5 bucks.The turkey pan being almost like chrome gets unbelievable attention at the car shows