I was thinking around 400hp would make a substantial difference vs stock and would not require much with good flowing heads. Small cam, good intake and I'm there. If I wanted to push it I'd go with tall single plane intake and solid roller cam + stroker kit. My experience with 340 showed me that it needs rpms to make it a fast car, but it would also drive great around town at low speeds. Granted, it cant be compared to my big block but it was to be expected.
We can get Edelbrock heads, but trick flows seem best value.