I don't know all the special needs for E85 (big jets, no rubber, etc) but CFM will be same for gasoline or E85:

CFM = (cubic inches)*(max rpm)/3456 * (volumetric efficiency)...

For street applications volumetric efficiency (VE) we use 85% for race applications use 110%... short cut/rule of thumb I use is cubic inches times 2 which is good for 7000 RPM in most cases.

I'm thinking a 750cfm will be just about right for you.... 850cfm better for all out racing.

For heavy cars (over 3000lbs) with auto trans street use you want vacuum secondaries (in most cases)... for more race application you'll want mech secondaries but still watch out with heavy cars and automatics, it can be difficult to get a good performance tune that gets anything close to reasonable mpg.

I'm partial to Holley's myself but that's just because that's all I've ever had and I kinda know how to get them close to right. There are a few manufacturers that have "E85" carbs but conversion kits are available to modify gasoline carbs to E85. Check with Summit or Jegs or your local speed shop to see what's available.

good luck,

-Chris