[fastd]

If you stay with the carb that you have (which should be fine - I have a 351w that puts 350 at the wheels = around 425 at the crank and I recently changed to a 600 cfm with mechanical secondaries from a 750 with vacuum); you should:
1. Get it dynoed for sure - it will take the guess work out of what you a trying to do - worth the $100-$200 to know that you are getting it right.
2. Make sure you have the right size vacuum springs.
3. You can add a secondary metering block so that you can change the jets if the dyno tells that your mixture is off.