Will cylinder heads off a 1997 Chevy 305 fit on a 1991 Chevy 350?

No, cylinder heads from a 1997 Chevy 305 will not fit on a 1991 Chevy 350. The two engines have different design specifications, including varying head bolt patterns and port sizes. Additionally, the 350 has a larger displacement and different cooling passages, which can lead to compatibility issues. Always consult an expert or reference specific compatibility guides when considering engine part swaps.