The 600 cfm should be about right even on a stock 350, the condition you describe, rich on a steep hill is due to the fuel bowl filling up and spilling over into the airhorn or even getting raw, unatomized gas into the carb passageways. Try a spring loaded needle and seat kit, I will try to find you the edelbrock part number if you will tell me the part number on your carb ie. 1405, 1406 etc?