E 650 carb
E performer Rpm vortech intake
E performer RPM Cam
E true roller link T.C.S  
GM cast iron vortech Heads
Hedman H.T.C headers
 

Doubtful. It's tough for a 305 to make more than 300 HP because of the displacement limits, and the long stroke. I'd venture a guess of about 260-275, which is mroe than respectable for a 305.  

You should make around 290H.P. with that combo.  

what combo should I run on the 305 sbc to make that much power and also how much will the gas mileage go down from 19 city & 23 highway.  

what is the part# on the vortec heads you mentioned  

#12558060  

Ok I would recomend a lunati streetmaster cam&lifters P#07101LK witch has a .477 lift and a edelbrock performer RPM air gap intake or a weiand air strike intake and the vortec heads you mentioned. Also I would use a set of self aligning witch are required for vortec heads roller rocker arms  p#66914 witch are 1.5 ratio and can be purchased from jegs for $186.  

I am going to use a edelbrock performer RPM air gap intake and the vortech heads come fully assembled on jegs.com.So should I still change the rocker arms and also thanks for the cam.  

yes because the heads do not come with the rocker arms and they require self aligning rocker arms and the roller rockers I mentioned will boost power even more.