My buddy Steve D @ Houston Performance is making ~350rwhp, and he's not even leaning on the tune up yet. Big bore 5.0 w/ his heads and cams, bullitt intake, longtubes, etc. Check out this months 5.0 magazine, there is an n/a stroker build up in there. Pump gas our engine made 375/385 on our engine dyno, using 11:1 c/r, streetable stage2 heads and cams, and a stock bullitt intake. This would be easily over 400/400 with more head work and camshaft. Even if we added race gas and tossed in some more timing we could've likely gotten close. It can be done, I'd personally use a 324 because you'll get the added cubes for torque AND the bigger bore for top end Hp.
Later
Scott