yeah, your on the right track.
YOu can buy aftermarket cylinder heads, and not have to do much porting if any. Becareful about any parts you buy, do your research.
I dont know how good you are at english, so some of this may be twice as confusing to you, but be careful about buying cylinder heads that are too big, maximum valve size in a 305 is 1.94" intake 1.50" exhaust. If your Port sizes (intake runners and exhaust ports) are too big that'll cuase a loss in velocity of the intake charge, and cuase a loss in low end power and driveability, almost as much as putting in too big a cam.
See the bigger the engine is (displacement) the more air and fuel the engine can suck into the combustion chamber, too big of a port wont allow any extra to be squeezed into the chamber (on a normally aspirated engine) instead will just loose velocity. Ever notice how on a garden hose how you loose velocity with a sprayer when you make the hole too big, same thing with an engine.
Hope i'm not diving too deep into this for you, but the more you know the better your chances of creating a very good combo.
Keep the cam selection around 215 degrees duration at .050" of lift. A hydrualic cam would work just fine, but you may consider a small solid flat tappet cam.