There are quite a few options out there but, frankly, even if you had a new carburetor installed dirt or other foreign objects in the fuel system will have the same effect as they did on your current carb. I suspect you've let the car sit for an extended period of time...
I'd first pull your existing carb, pop it open and see what's inside. If you have a lot of sediment and a buggered needle & seat, replace it and then go track down where the sediment is coming from. If it's a Holley, consider installing the sintered bronze inlet filters for catching the very fine crud.
You may find out that something like a power valve diaphragm or accelerator pump check valve has deteriorated from an ethanol-blend fuel during the extended "rest period" and needs replacement with an "alcohol proof" version.
No sense tossing the baby out with the bath water.
Yep, the fuel blend these days plays havoc with a lot of things. If fuel is leaking out of the throttle shaft, it is more than likely a float issue. With the engine off, can you see fuel leaking from the vent tube or further down inside the Venturi?
If it is, a careful whack on the fuel bowl (with the wood handle of a good sized screwdriver) can unstick a float.
Pull the Holley, pick up a rebuild kit from AED Carburetors (Summit, Barnett Performance and even Amazon have them) and go through it carefully. Clean and replace everything. Itís an eveningís worth of time.
Post the Holley carburetor list number, and we can suggest the correct kit.
But yes, with an automatic you want no more than 600 cfm and vacuum secondaries.
Holleyís are infinitely tuneable, but darn close out of the box 95% of the time.
The extra filter is a good idea, as would be flushing the gas tank if it hasnít been done in a while. Something is messing with your carbs; they all canít be acting up without cause.