No way you're gonna be 400 at the wheel, that's roughly 450 at the flywheel. Anubis has a 6.0L in his Cutlass and with the efi tuned he's at 420ish. Carbing an LS eliminates alot of tunability and loss of power.
The LM7 in my Cutlass has 862 heads with BTR .660 springs, a .613/.598 lift cam, stock bottom end, headers, 92mm throttle body with Holley intake. I'd love to see 350+ at the wheels once tuned before boost.