Those bed bolts appear to be the aftermarket ones from Mar-K? Did you replace them?
I used I believe a #4 Phillips with 3/8" drive...with a broken tip no less. I think a #3 will work in a pinch, but they're even bigger than #4 anyway...
You could call Mar-K in Oklahoma and ask them what size you're supposed to use on their 1/2" bed bolts.
1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995