The original 305 that came in that car was rated at about 165hp. The mods you speak of may get you to 195-200 hp. It takes a lot more than the mods you mentioned to get a 305 to 300hp.
That's why so many people use the 350. It's a much better base engine. The small valve heads and small bore of the 305 doesn't lend itself to small mods/big hp.