I dont think you are going to gain that much from a 4bbl carb swap, maybe 5-10hp, not enough to really notice any difference. You would be better off spending the time and money on tuning the engine. Maybe some hotter plugs, good plug wires, timing. Depending upon your experience level, you could lash the valves (adjust rockers). Rebuilt and jet the carb which is on the motor now. With all these properly tuned you will probably gain as much, if not more hp than replacing your 2bbl, and for allot less money! By the way, the stock HP of your engine was 160HP at 4000rpm's.