That plate keeps engine heat off the floor of the intake plenum. If you remove it to clean underneath, try to find a safe way to reattach it. It'll keep the air a tad more dense.
Thank you - that's good to know! Maybe I can bend it a bit to get underneath, because all that build-up can't be good either. It's not gonna stay on for long anyways, because once I know how much everything cost and I can justify buying a carb, I want to install the 4 barrel manifold again.