Edelbrock said that manifold is a direct replacement for the 4V HO manifold. That being the case the exhaust gas comes up through that hole and into the EGR valve itself. Lots of guys on here have made block off plates with everything from a Coke can to stainless steel sheet. You will need a gasket on the manifold, your block off plate, another gasket, and then the carb. And the bottom gasket has to fully cover the hole, as does the plate.
Rusty: '81 F150 Ranger XLT 4x4 w/a 351M, RV cam, Performer carb & intake, C6, & 3.50's
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads, Weiand intake, Street Demon 750/ZF5/3.50 gears w/Kevlar clutches
Worst fear: I die and my wife sells my trucks for what I've told her I have in them.