You can always claim 400HP.. EVERYONE these days has / wants 400HP, so call it that.
Then you take this 400 HP motor, run it on every day gas, with normal underhood operating temps, with normal accessories like alternator, water pump, power steering, losses through a cheep converter, and the input shaft of the trans really sees 325 or 350 at best.
Here's a sbc 400 with those very 170cc Edelbrock E-tec heads, a RPM Vortec airgap intake, Comp 284XE cam, Prosystems 780 carb, TH350 trans and 4.10 gears and 8.5" slicks. ET / weight said it made close to 500
http://www.small-block-chevy.com/dana1.JPG
rbl,, I ran a set of the 6071 RPM heads on a 350 long ago. Stuffed a bunch of nitrous through them,, there a solid piece. There a very nice street head. Edelbrock concentrates on port volocity and doesn't advertise a bunch of bogus inflated flow numbers. Partly because their flow numbers are not very impressive. And to build torque, in a streetable combination, big huge flow numbers arent what you want anyways. The RPM head has great mid lift flow and port volocity,, very capable of 1HP per cube in the typical 'as installed' combination at streetable rpm's (meaning WITH water pump, alternator, PS pump, typical underhood temps, windage, etc. etc. etc.)