One thing you must keep in mind with a fuel pump in a C3 Vette is the hook up of the fuel lines, best advise is to use a pump that would have come on a 70 LT-1 or a 69 Z/28, this should fit properly and you would be able to hook up your fuel pipes, IF you go aftermarket the ONLY pump of choice is a CARTER, with these pumps you can clock the inlet and outlet parts of the body to allow proper hookup and they will fit in the limited clearance where the fuel pump sits. I have tried almost every pump made over the last 40+years and have found the Carter to be the best, and it will not run out of gas on long runs in high gear. When you change the pump make sure you use a lite weight fuel pump push rod as well, they help at high RPM, I have had the same Moroso Push Rod in my car for over 30 years , used it from motor to motor over the years and still NO Issues.