As far as I know, the rules only ever called for fenders on all 4 tires. It never specified what type. Aero was not a big concern at the speeds we were running in the 60's. The advantage the cycle fendered cars had was the fenders were lighter, and they could use class weight on the rear for ballast. My car was 100% steel Ford, and still needed 80lbs of steel plate in the bed to make class with 301 cu in. I never even considered anything but the stock fenders.