Hey Ken P. I own an original 69 Impala SS427 with L72 425 hp 4 speed with vacuum power brakes. The vacuum come from the back of the Holly carb. The engine produces low vacuum and the brake pedal gets very hard after a fast stop. I am installing a pump from Summit Racing to correct this fade. Do not use a cheap one as they are noisy and do not work well. Maybe get a better booster than original. NICK L72