You cannot jet a carburetor down in cfm (ie: from a 750 to a 600). The size of your throttle blades and venturi are fixed and, in addition to the flow restriction posed by the boosters, are what determine the cfm rating. What you can do is adjust the the jetting to achieve the appropriate A/F ratios. You are in luck, because Edelbrock carbs have to be the hands down easiest to tinker with. Get a hold of an Edelbrock carb owners manual and read it thoroughly; it contains everything a beginner needs to know to get started tuning.