.A 496 (4.310"x4.25") or a 509 (4.5"x4.0") with Merlin 310 or AFR 305 non-cnc heads(Merlins about $1200, AFR about $1900), Edelbrock Air Gap, Barry Grant carb (talk to rumrunner), DUI ignition, Crane 741 cam. Properly prepared, this will give 600+ and live forever if you take care of it. Longer rods, bigger bore, custom cam, better heads, etc. will get you more, co$t more. Iron heads are cheaper, aluminum more forgiving, AFR makes noticably more power, tolerates fuel octane better.
HOTRODTODD, give us some info. You don't necessarily have to build a motor to make it live with a blower unless you have too much compresion, poor fuel, or cheap pistons You might pick up a blower cheap and make a killer yourself.
Even with lower quality fuel, some things can be done, if that is a problem where you are.
Whipple installs are not very difficult. Just follow directions. Dustin can usully answer almost any question. If you can swap intake manifolds, you can do the whipple. Heck, even I can do one.

My vote is the 496 it is cheap and easy and very dependable
,if you spend the money for a block its just as cheap to do a 565 and that would be a terror , 600 with either of these is easy !!
or buy a crate 502 and change to a 741 crane cam and fix the heads 8.8 or 9.0 to 1 comp .and theres your 600h.p. cheap and easy
you still have the factory motor to but back in to sell when you buy your outerlimits