Will a1992 Chevy van bumper fit a 1981 truck?

No, a 1992 Chevy van bumper will almost certainly not fit a 1981 Chevy truck. The body styles, frame dimensions, and bumper mounting points changed significantly between those years and models (van vs. truck). Even within the same body style (e.g., comparing two Chevy trucks), bumpers often don't interchange between model years.