Will the heads off a 2002 Chevy silverado 2500 6.0 fit on 2000 engine?

No, the heads from a 2002 Chevy Silverado 2500 6.0L will likely not fit on a 2000 Chevy Silverado 6.0L engine. While both are 6.0L engines, there were design changes and revisions over those two model years. The cylinder heads themselves may have different bolt patterns, valve configurations, or other incompatible features. You'd risk significant engine damage trying to force a fit. You must use cylinder heads specifically designed for the 2000 6.0L engine.