Looks like a 600 CFM would be just about right, and yes throttle response would most likely improve. Might want to try your initial timing at 8 to 10 degrees and all the timing in by 2200 to 2500 RPM with total advance around 32 to 34 degrees. Should give you a good baseline to tune from. Watch for detonation closely, then do some plug reading and jetting corrections on the carb. I'm really getting spoiled, after the initial run-in I do my tuning on a chassis dyno. Takes all the guesswork and trial and error out of it....