Carbon Monoxide

I feel after driving my 68 Cuda that I am experiencing symptoms that might be brought on from breathing in carbon monoxide. The exhaust system from the engine to the rear bumper is new and has zero leaks. The trunk seal is new, actually all the seals on the car are new and the car has zero rust anywhere. Car is a show car, is it just me or is this the norm when driving a car that never really had emissions on it from factory. I had other muscle cars in the past and never had this problem. I'm at a loss considering I can't find a breach anywhere on the car where the exhaust can enter, other then driving with the door window down.
i'm actually thinking about obtaining a hand held carbon monoxide detector to verify when driving the car.