picking carbs

i am going to eventually have a beefy 350 in my truck capable of over 400 horsepower and i am deliberating what type of secondaries to go with... since its heavy and relatively geared for low-rpms, should i get vacuum secondaries? it will have a comp cams 262 hydraulic flat tappet cam, so it will have decent but not excellent vacuum, somewhere better than 10-12 at idle. would i just have to swap out the power valve to one that opens at less vacuum since the carb is prolly configured for stock vacuum levels?

any ideas and suggestions muchly appreciated, thanks

A 600 cfm vacuum secondary carb will serve you well. A 350ci engine flows approximately 550cfm of air at 5500 rpm, so you don't need anything bigger. A larger carb will cost you throttle response and more gas. I had a 81 cutlass with a 355 that we experimented with. With a 600 cfm holley vacuum secondary, it ran 13.2. We switched to a 750 double pumper, and it fell to 13.5 and lost 8 mph at the high end. Most people WAY over carb and over cam their engines for the intended use, because big numbers sound better and will make it go faster.......WRONG.