[Big-Foot]

If you do this "BEFORE" you expose the floats to fuel, it will work;

Carve out the section of the float that interferes with the whistle by using a dremel tool. Now, mix up a batch of the good (takes 8 hours to cure) JB Weld - don't use the 1 hour stuff - and carefully paint over the area you just carved out and have a little over the edge to "seal" the float. It will work. Nitrofill floats are impervious to just plain gasoline, but Octane Boosters are another matter.
Frankly - I would just trim the whistles a little and connect the two bowl vent tubes at the top with a short length of rubber tubing and put the vent holes in the top of the tubing. Well - That's my $.02 worth anways..