Not sure how it is "mouse-proofed", but I'd recommend getting an air cleaner box with the tube that goes up to the radiator support for cool air. You should be able to find one of those at the salvage easily.
The illustration below is what you should have, but there's a later one that instead of tube 9A624 attaching to the radiator support down low it actually lays on top of the radiator support. So either of those would work.
Having said all that, I highly recommend you do not go with an open element air cleaner w/o the box and cool air tube. That's because you'll be sucking hot air into the intake, and that will reduce your power.
Gary, AKA "Gary fellow":
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Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI