Do not buy those heads. they are the China casting heads that they re-work..
Spend a few hundred more and get a set of Edelbrocks,,,, you will thank me for it later.
Hp guess is just that, a guess. You can run the numbers on desk top dyno and get 575 hp...then strap that engine on a real calibrated dyno and pull 425 hp...
There are just way to many things that dictate what hp the engine is going to actually make.
I ahve a program that if you tell it the truth will get you with-in 3% of a calibrated dyno for HP,but i need way more info then you gave to even start entering numbers.
At 17 years old my question would be, how much HP do you need, and what do you need it for???