A run of the mill 383 is not going to get you there, stroked out to a 496 yes. A 440 can get you to 500-600. You're gonna have to punch her out to get it on the higher end of the 500's. Either you can spend a boat load CNC milling the stock iron heads or buy some Edelbrock performer's or mopars aluminum version standard porting for a cheaper price than dealing with the iron.. An extra plus to the aluminum head is its going to give you more leeway for using pump gas. Your gonna need good breathing heads.You don't need to go all out like B-1's or crazy Indy heads..Too much head for your engine is not a good thing for more of a street car because they will not produce you high torque levels at low speed, but will produce high horsepower at high engine speeds. More of a drag car senario.
One senario i've see work out well for your 500-600 range is run a 4.250" crank, 6.8-7.0 rods, punched RB block at 4.375, good breathing aluminum heads (265-290cfm), Hydraulic roller cam around 240 Dur@ .05, with a 600 lift, 10:1 dished pistons, a decent RPM based intake, 850-950 carb and some good 2" headers pushing it all to the rear. You can get away with a pretty well behaved 750RPM idle this route.
I'm sure a lot of other guys here could also share their formula's to help you along. Just something that's worked for me and others I know. Bottom line to you your question, there's no replacement for displacement, and the longer stroke of an RB makes it easier to bump up your torque/horse in a hurry than a B. You're much better off with the 440
Good luck!
Also to add to 1badgtx 400 idea, you can punch the 400 out to 4.375 like the 440 and have yourself a low deck motor if you're worried about hood clearance issues.
