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It goes between the air cleaner and upper radiator intake shroud. ;-)
That is an anti-splash shield. Its purpose is to deflect water so it doesn't get sucked into the air filter.
I bought one a few years ago for my '86. It was too much trouble and I never had a problem before I installed it so I threw it away. It was introduced around 1990 or so. If you don't drive fast through deep puddles you don't need it.