Couple of things.
Right to start with NO ONE can tell you anything about how to set that carb up without ALL the information. Engine specs, including thte compression ratio, heads, head flow, intake, exhaust, etc. Transmission and converter/stall speed or stick shift? Gear ratio? Vehicle, weight, suspension, tires used.
This thread should also be over in the "race" section because a 400 with that much cam is going to need a LOT of compression to make much beyond 5" vacuum at normal idle speed, and WAY too much cam for 99.9 percent of the 400's that would be built for pump gas/street use.
As far as tuning on something you just bought, initially I wouldn't touch it with a 200' pole.
Install the carb, make sure you have adequate fuel delivery for the power level, and do some testing. Evaluate the carb in all areas, then go back and make changes to those specific areas that need help. You may not have to touch it, but in my experience (I've built a few carbs here and there) it's rare to have anything come right out of the box and be spot-on in all areas with a smaller CID engine with that much cam in it........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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