If you build a 355 with 400 HP, the 750cfm will be fine. But with just an intake,carb and cam swap, you have quit a bit to go before 400+ HP.
You'll need to spend alot in heads, pistons,bottom end work,valvetrain,ignition,etc before 400+ HP comes around.
But it sounds like your off to a start.
383 Speed-O-Motive stroker kit with Speed Demon 750, RPM intake,Proform HEI dist.MSD6a box,World Products Sportsman II heads, ported and polished with 2.02/1.60 valves,64cc,TRW forged pistons with 10.7:1 compression, Comp Xtreme 284 cam,Crane pushrods, Comp Cam 1.6 full roller rockers,ATI damper, 40 series Flowmasters, 4.11 gears with TH350 and Hughes 3000 stall.Powertrax NoSlip Locker