for 550 hp reliably and most economically...I'd say the 511 B or RB motor with bowl worked E heads and a 255 @.050 .600 lift cam, A St Dommy intake and an 850 carb. I said Economical in terms of least $$$ for the Bang...nothing done right and built to last is truly "cheap".

Buy the E-heads off somebody that just upgraded to Max wedge heads (like many eventually do)

Nothing exotic about the shortblock kit, just top notch machine work and careful assembly.

Easy 550hp, and yes, you can get 550 out of a stock stroke 440 or 451 B....but your streetability will be more reliant on a looser stall and deeper gears. If it's a bracket only car you can surely get there and the streetability isn't an issue.

Case in point...I just did a 414 small block, horse trading parts and a a used solid roller cam I'm pretty safe telling you it makes an easy 550, I can also tell you it cost about $1200-1500 more than if I did the 'economical' 511 I just described above....The extra $$$ is typically in the needed head porting plus the typically higher grade valvetrain you need to reliably spin the motor high enough to use it.
But a B motor don't fit too well in my car. Don't get me wrong I love it but at 500-600 Reliable HP a B/RB is the way to go...the reason is mainly the heads, Small block heads can make that kind of power...but not really out of the box. conversely, I'm pretty certain just about anybody can make 550hp easy (and with broader overall torque and less RPM) with a set of BB E-heads on a 470-up motor pretty easy.....with nothing more than and ultra streetable 235 ish at .050 Hydraulic Flat tap.

Horsepower targets are typically all about head flow requirements...with less regard to cubes (when you make it up with RPM), torque curves and how you wish to apply it to the ground is really a completely different (and application specific) arguement.