Holley 650 ultra double pumper

I have a 340 with a pretty big cam (not sure on specs, unfortunately), single plane intake, ~9.5 or 10:1 comp., stock J heads (larger valves), and headers. Do you think this would be big enough to feed that? I'm not too familiar with the double pumpers. I have a Holley 3310 750cfm carb with vacuum secondaries and I heard that this could be replaced with a 650 double pumper.

Also, when was it last run? Has the fuel been flushed out to maintain the seals?
Thanks

-Mike