Thanks for your comments 3304hl. This car has what I call a 3/4 belly pan. From just behind the front seats to about six inches forward of the rear wheel openings there is a gap in the belly pan. This section of the underneath of the car is already very flat and by not having the belly pan full length, it allows the engine compartment to vent out the back of the front portion of the belly pan.
Here are some pictures
Also note that the muffler has been relocated to the space where Honda places the catalytic converter on the civic CX and EX models of this car. This allowed me to make the rear belly pan and diffuser much smoother. This location already has a heat shield and I also added extra heat insulation for the "cherry bomb" type muffler. It seems to be just as quite as the original one.
My other car, the red mule 92 VX has a full belly pan that vents out the very back of the belly pan, but when you stop after a trip, heat is retained inside the pan and it radiates up into the cabin.
Also the white VX has adjustable shutters in the grill, which allows me to regulate the water temp of the engine. I adjust the shutters to maintain around a 190 degree water temp and oil temp at all times.
I have installed an air temp sensor inside the engine compartment just under the intake manifold between the firewall and the engine. So far this summer the highest temp I have seen in the engine bay is 142 degrees. To my surprise, the highest temps are seen when the shutters are fully opened. I guess this is because when more air goes through the radiator full of 200 degree water, it actually heats up the engine bay more than when less air is flowing through.
Also remember a lot of air is exhausted out the front wheel wells.
One other comment I would make is that most of the year I struggle to even get the oil and water up 190 degrees with the very cool running lean burn engine in the VX. So except in the summer, all these modifications are needed to retain heat and I am not concerned with exhausting heat.
Hope this answers your questions.