Intake manifold

I have a 93gmc 5.7 V8 , on the intake manifold gaskets the rear two ports
are blocked off ,is this normal.

I remember when I took them off that the rear right was blocked off, but
cant remember if the rear left was.

When I say blocked off, I mean the hole on the gasket where the port will
line up is blocked off by a aluminum piece, is this normal?

Thanks