Best to sand blast it out if you can . At the very least , wire wheel as much of it out as you can and treat it with a mild phoshoric acid solution. If your not comfortable mixing up your own go to a auto body supply and buy premade metal prep. Let it soak good , wash it off, then prime.

85' 4x4 e-cab flatbed 22r carb ((SOLD))
86' 4runner, 22re , "60 buck truck"
95' 4runner, 22re,5sd, last of the good ones
02' Tacoma prerunner, 2.7L, 5spd., 4x4