Regardless of the pump rating the problem with trying to use a mechanical pump to feed a big CID powerful engine in a pretty fast car is delivery to the pump.
I can tell you from actually doing it that 40gph or 120gph isn't going to much matter trying to feed it with 14' or so of 5/16" fuel line (the inside diameter of 3/8" line BEFORE you bend it). It is ALWAYS better to push the fuel vs pull on it. This certainly makes modern in-tank pump systems the way to go if and when the goals for your vehicle include a powerful engine and steps for the car to make HARD runs with good traction.......FWIW.....
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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