I would search for a good set of used heads, intake, throttle body setup if you only have 4,000 for the whole build. Buying new is kinda out of the question since the heads alone are around $1,800, $800 for the Intake/TB setup. That's $2,600 right there and you are still missing a crap load of stuff. I'd go a 393w and even if you had to put AFR185's on it, the car would still fly.
Best bet is get whatever you can used in good condition and work with that (Trickflow R, AFR 205, etc.)