Oh! That makes a difference.
You said it is in a gear but you don't know which one. Have you moved the truck since getting it back together? If not, I wouldn't try for fear that the transmission is in two gears at the same time.
I think I'd pull the driveshaft and have someone push in on the clutch and see if I could turn the output of the transmission by hand. And if you can try to work the levers to see if you can get both of them operating.
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