Yeah, sounds like a vacuum leak. Check around intake and carb base. Spray carb cleaner ( be careful not to spray on distributor) around gasket areas and engine will smooth out if you find a leak. Also make sure float levels are good. That cam should have at least 10 to 12 in of vacuum at idle. I wouldn't go for the factory spredbore with that cam. The holley if working properly should be great ( except for gas milage ). Also intial timing should be at least 12 to 16.
Bill