Putting an open spacer on a dual plane Intake like the Edelbrock Performer changes the way the engine behaves more into the way it would with a single plane Intake. Putting a larger Spacer on it will increase that behavior.
Common knowledge is, that a dual plane Intake increases low end torque and lacks top end power while a single plane does it the other way around. The reasons why can be read above. Basically it all depends on where you have the best air flow.
What also has to be considered: The vacuum signal gets worse, as you increase the volume of the plenum. The same happens to the booster signal in your Carb. So less fuel gets pulled through and your air/fuel mixture gets leaner.
You could consider a 4-Hole-Spacer for example, but what definitely should be avoided are sharp edges or any sort of disturbances of the air flow.
If you want to read more about this:
https://www.motortrend.com/how...-carburetor-spacers/
And as always: Sorry for my bad english