That depends on the year. The 4.3 went through many changes over the years, including the addition of a balance shaft somewhere along the line. 1994 to '96 I believe was the timeframe. The people to turn to if you want solid answers would be an S10 forum. Astro, S10, full-size pickups, Monte Carlo, Caprice, are all good sources to find 4.3 V6. Head gaskets are NOT a common issue with these engines. Does yours have TBI or is it carbureted?