stock motor with just basic heads cam intake / bolt ons is around 270-300rwhp.
If you want over 300+rwhp some with tunes and longtubes see 300+ like 310-320rwhp with the trickflow , afr heads.
I will use my cars 3 setups for example.
My car with the stock 302 motor with trickflow heads,Fcam trickflow street heat intake shorty headers basic bolt ons, put down around 273rwhp. with a tune and upgraded the throttle body from a 65mm to a 75mm and changed few small things and pulleys it was right around 295-300rwhp.
My new 306 c.i motor with more compression new pistons/ rings. much bigger comp cam, ported trickflow trackheat heads and intake long tubes etc is around 330-360rwhp. last time on the dyno with no compression in cylinders 1 and 2 bad rings and valve seals it still put down 295-300rwhp lol motors rebuilt now. so should still be around 330-350rwhp. ( I hope) But not planning on touching it dynoing it leaving it alone now.
So that being said stock motor with heads cam around 270-300rwhp is where you should be at.
but if you go with stock ported heads or gt 40 heads. small e cam or small cam your not gonna make over 300rwhp. 240-270rwhp.
SO you deff want a nice set of trickflow or AFR heads to do it.
a nice 306 or 331 stroker /347 stroker with same heads cam should get you around 350-400rwhp.
food for the thought