Not saying this is the rightway to do it, but when I set mine up for the 1st time it was on a 11:1 440 w/ a 528 solid cam lashed tight. I checked the floats before I installed the car..how? I flipped them upside down...hahah I primed the center carb only, left the out boad rods unhooked, turned the mixture screws all the way in then back out 1.25 turns...I set my full timing then initail and finally tuned for best vaccuum at 800rpm. Then I hooked up the outboards. I checked the floats, they were a tad low but not enough to worry about. I shut the car off, then I had my son floor the car and I opened the ooutboards by hand to make sure I had 100% throttle. Worked fine.
Usually when holley carbs "dribble" as you state the floats are high. That or you need to adjust your outboard rods. With your cam your outboards should be shut, you shouldn't need to drill the holes any bigger. My cam has a duration of 292/297 (254/260@.050) and I didn't need to open mine up.
I think you are close, you just need to fine tune it.