You don't need anything that expensive or fancy. In fact, that adapter probably won't work due to the linkage bracket mounted directly behind the 4A1.
Try this. Go to any Autozoo, CSK, NAPA, Carquest and get a standard 4BBL to 2 BBL adapter
Use the fiber spacer as a template for the mounting holes. The front holes will line up but you'll need to machine the rear holes.
Here's how it looks machined
and here is a bottom view with a 2 BBL Autolite carb mounted.