Neither will be cheap or easy to get 400+ rwhp normally aspirated but there are a few DOHC guys that are there already, namely with PnP heads,cams, FR500 intake, LTs, with the right supporting bolt-ons so it is possible. I dunno about the 3v but I'm sure they're well on their way to some serious n/a HP especially with their popularity of the new model.
Check out this guy on mach1registry with a 99 Cobra and built 304 CI, 459 rwhp motor normally aspirated...
N/A Cobra taking down a Terminator with the usual Intake/Pulley/Chip/Exhaust