its hard to get 400 HP out of a SBF, it can be done, but the heads and cam required to make this power operatie WAY UP in the rpms, like around 7 -8k, by the time you get it making that power, the car will be a DOG down low and wont be any fun to drive, wont be a good daily driver either.
if you want to go the N/A route, start with a 351 block, a stroked 351 will be able to make 400 horse alot easier and more effieciently than a 302, 347 could probably do it, if you want to spend the money.
personally to get 400 horse out of a small motor efficiently and still have good street manners is a power adder IMO.
a 302 with a good HCI, and 8-10 psi with a centrifugal hits 400 pretty easy. stroke it and it really starts making power.
nitrous is also a good power adder. has more of a KICK in the ass as opposed to a centrifugal supercharger building up power as rpm increases, but the downside is your power is in the bottle and more of a hassle to mess with it. where your supercharger runs all the time and makes boost when you need it. plus if you get hardcore with the n2o, after a year or two of filling up bottle you could've bought a SC
grab a trickflow HCI kit, throw an s-trim or novi2k on it running 8-10 psi. and you have a FAST car, making 400 horse, that'll run 11s. that will drive good on the street. and could be used as a DD. if you want to make some insane power. get the stoker kit you mention, rub some low compression pistons, and bullet-proof the bottom end and start spinning the SC to the moon and make 15 psi. you will be getting with it then.
under normal driving it will act like a n/a car ( but wont be a terd, since there is the stroker bottom end with a good HCI), once you cob down on it boost takes over and you take off like a rocket.
you could also fab up a turbo setup, usually takes more tuning expierence and more money but when done right a turbo rules all.