i've built this engine. yes, it makes 400hp but just barely and if you look at the dyno results you'll notice that it has a narrow, peaky powerband.
it's fun, but that wears off quickly if you've got a 4spd because you're always stirring the pot looking for that sweet spot of power. it makes less power but is A LOT more driveable and well mannered with a dual plane and a more reasonable carb.
anyway, it's not as cake of a build as they make it out to be. a ton of little details that need special attention. and the machine work must be *on point*. and without headers, this probably makes 370/340.
nice lopey idle tho.