Are you talking about the .090-.100" thick plate, shaped like a base gasket?
If so, that is to ensure the edges of the gasket seal when the carb is mounted to an intake with a dual squarebore/spreadbore carb pattern....otherwise, there is a good chance of a vacuum leak occuring at the carb base on eather side of the area where the wide secoindary barrels section is on the intake manifold.
It doesn't need to be used if the intake manifold is a square bore pattern only.
The Edelbock likes modest fuel pressure at or a bi less than 6 psi so mounting a gauge to keep track especially if using a performance fuel pump is a good idea.
The Edelbock also doesn’t like a hot intake, you should plan on using at least a quarter inch but better a half inch thick insulating spacer between manifold and carb. Without this it has a habit of boiling the float bowls dry after shut off.