Carb CFM help

I'd just about settled on the 3310 or the 80783 like was suggested before hand, so looks like the research over the past few weeks was close!

What would be the benefits of the double pumper over the vac. secondaries?

We may have a 3310 on the shelf in the garage, and I know we have a ton of rebuild kits. I'll check on that one when I get home. If not I was planning on heading out to the Pomona Swap Meet this sunday to try and find something. $300-$400 for a carb is a touch out of range at the moment...

Thanks very much guys!