80/ F-U100/350 E0TZ 17696-D
Kit: R.H. & L.H.-dual position stainless 6" x 9"
The "80/" means 1980 to the end of the master parts catalog, which is 1989. So yes, they will fit an '81.
And that part number is for a kit, with both left and right mirrors.
Gary, AKA "Gary fellow":
Profile
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