Or it could be a '72 455. What is the date code on the rear of the block next to the distributor? Should be a letter and 3 numbers. The last number will be the year and that along with this info will tell you what it is.
Oh, and that Holley isn't a Double Pumper. That's a 750cfm vacuum secondary. Actually that wass probably one of Holley's biggest selling carbs for steet engines.