Can yous a 1981 Chevy truck bed on 1992 Chevy?

No, you can't directly use a 1981 Chevy truck bed on a 1992 Chevy truck without significant modifications, likely more than most people are willing to undertake. The body styles, frame dimensions, and mounting points are substantially different between those two model years. The wheelbases may also differ. Even if you could manage to make the bed fit, aligning it correctly and securing it reliably would be a major project.