So as soon as I put in the intercooler and had to take out the foremost air duct that directs air to the radiator I began running hot. It wasn't a violent overheating or anything. It was just that on the hottest days 105* or so the car's cooling system passes a threshold where it can't shed the heat fast enough. It takes about 15 minutes for it to get there but usually at the point where I cross over a river and up the incline of a bridge I have to turn on the heater full blast to keep the needle from going up anymore. I chose the point at which I can see black between the needle and the little wings on the thermometer on the gauge, so about 3/5's up on the gauge. Anyway check this splitter I made out of 1/8" polypropylene. Came out a little better than I thought but I still have the holes pictured below.

So, have I done enough to direct the air or am I going to have to make some pieces to close these openings off?

 

You have to close those openings off. The air WILL take the path of least resistance. Just continue with what you've done on the bottom.