I think the solution to your under hood temperature problem could be solved using a little different approach. I would like you to read this article that I found a long time ago. I learned this lesson on a vehicle I was troubleshooting years ago. Trust me the missing air dam when replaced made a huge difference in the temps I was seeing. You will probably have to experiment with the placement of the air damn to find the optimal position and height. Air dams are used on most if not all cars nowadays and the bottom of the engine compartment is somewhat sealed. I would also like to add that the a/c outflow temp should be much lower than 57 degrees (I usually will not allow a car to leave my shop if over 45 after an a/c service). By your description I would suspect that your system is overcharged. Hope this helps! Ray

The problem
The impeded flow of air through your radiator and engine compartment. What engineers found was that the configuration of the body forces a strong current of air directly under the radiator, a flow which does not simply pass under the car but flows up into the engine compartment where it collides with the firewall, causing the air to back up in the compartment and create a relatively high air pressure inside it. If air inside the compartment is exerting even the slightest back pressure, it will inhibit the flow of air through the radiator. The higher the speed, the more pressure and more impedance, and at high speed, this can be substantial.

The answer
Block the area directly beneath the radiator down to the bottom edge of the frame with an air dam, preventing that unwanted flow of air into the engine compartment and thus greatly increasing the efficiency of the flow of air through the radiator at speed.
The best design for this simple air dam we've been able to come up with uses a piece of rubber floor matting available at most hardware stores. This is fixed in place with bolts that hold the radiator to the frame beneath it. The rubber matting, after it is bolted on, can be draped over the steering rods, and will not interfere with their operation. It must be long enough to extend the bottom of the frame. As the air hits this dam, it will force it into place in front of the suspension frame just behind the radiator. Above 25 m.p.h., this system will really work. The relatively low pressure inside the engine compartment pulls air through the radiator and down and under the car. Side benefits include:
1. Reduced engine fumes inside car.
2. Cleaner firewall and engine.
3. Improved cooling, as it can no longer pull air from beneath the radiator.
4. Lower under hood temperatures