From reading the testing news, the exhaust changes are not Road Course vs Speedway, but trying to deal with the cockpit temperature getting excessively hot. I wouldn't be suprised if the circle grills are for extra brake cooling, as NASCAR road race cars have had extra cooling ducts on Short Tracks and Road Courses since at least the 90's, though they are still making pretty significant changes to the car and the package, so anything is possible at this point.