Next is an intake and 4 barrel. Too bad dyno time for this kind of thing is so expensive. I bet someone has already done the comparison. Then headers and tune the carb to it. The next step could be a cam unless you wanted to go for better heads and a cam to match. That may include a performance torque converter and/or rear gears to make it work. Depending on where you start, you may be able to add compression with the right heads. Smaller chamber, bigger valve, better flowing ports is a win/win. The last combination would be a stroker. It might not add a ton of horsepower over the head/cam build but it will add more torque and at a lower rpm which is more usable on the street. May be the next level would be turbo or superchargers? Let's not go there though. Not in this thread.