I have 2 different carbs that I can use. 1 is the 80457 (600 vacuum secondary) and the other is 80508 (750 vacuum secondary duel feed). The car is going to be an automatic with a factory h/s torque converter. The motor is a .030 360 with 10:1 piston, .484 purpleshaft and the heads have been rebuilt with 2.02 valves and some mild cleanup. The rear gears are about 3.25:1 with a 235/60/14. This is going into a 63 Valiant convetable. The car will be more of a weekend cruiser and just to drive around when the weather is nice. I will also make a couple trips a year to the track and the occasional exhibition of speed, but for the most part, just a fun car. Looking for the better of the 2 for power and mileage. Either way, I need to put a kit in whichever I use, so I am looking for which would be better to use.