I need a little enlightenment on this Holley carb

Looks like you already have the after-market EGR block-off plate (~$20). Save that to use on any later intake. You will have to get a special "Super Six" 2 bbl intake (~1976+) to use a 2 bbl carb, and almost everyone uses the Carter BBD for that. But, those intakes are getting rare and expensive. For about the same price, you can get a 4 bbl alum intake (Clifford or Offenhauser). A 390 cfm 4 bbl carb can conceivable give better mileage than a 2 bbl. For super-bling, the Aussie Speed Hurricane 4 bbl intake can't be beat, but >$500.