I dont see how the wheel wells are a low pressure area on these cars. Unless my car is missing some parts, very likely, then there is a huge pocket where air gets traped directly behind the front wheels. Cutting a hole in the exterior metal and venting it outboard will promote smooth airflow. That or install an inner fender shroud like most modern cars have.
Another idea that I had was to reduce the drag created by the headlight buckets. If you can move the acctual headlight foreward by an inch or so that will allow air to flow around the light and into the inner fender. This air can then be vented overboard through the wheel well or just aft of it. Or if you really want to get creative duct it down to your brakes, the more air on those the better. btw, moving to a smaller diameter light in combo with this mod will get more of that air out.
The only way you will be able to get your car up to and past 200mph and not feel like it's going to fall apart is to completely rebuild it from the ground up, new suspension, up to date aerodynamics, basically redo everything.