Yes better heads will make more power, but stock gt40s will make plenty to push block to its limits.
I have a 302 stock block, stock crank, forged rod and piston, stock gt40 heads, intake, throttle body, etc. Anderson n41 cam with on3 turbo kit. On 10 psi I made 520 rwhp. On 13 psi, we didn't make a full pull on dyno, but made a pull to 4800 and would have made approximately 600-620 rwhp..
So, yes, itll make more power with better heads and intake, which will let you run less boost for same power, but it is definitely not needed
So, better