I saw a lot of cars with those on. That is a strip car, My SS427 Impala was a street car. Excellent traction and I didn't have a rear sway bar with M21 and 373 posi. I am adding a hotter cam and headers with sway bar and adjustable shocks with a dual pumper. I wonder if they used roller rockers and changed the valve springs. Chevrolet changed a lot of springs for Me and even a ring job during the 5 year 50,000 mile warranty. It still burned a lot of OIL. I guess I over revved it too much and did not brake it in. Too much fun on the Street though. Rebuilding it after 50,000 miles with Comp cams parts. At least Mine goes around the corners and is Le-mans Blue. NICK L72