Edelbrock 500cfm on factory 273 4 barrel manifold

A previous owner rebuilt this 1965 273 to commando specs and installed the factory 4 barrel cast iron manifold and a new Edelbrock model 1403 CFM carb. Seems to fuel really well. Any idea if or why it required the 1/2" thick aluminum spacer between the carb and manifold? I'll post a picture later. Thanks