Will Vortec 350 heads work on vortec 305 engine?

No, Vortec 350 heads will not directly work on a Vortec 305 engine. While both are Vortec heads, meaning they share a similar design philosophy, the bore spacing is different. The 350 has a larger bore spacing than the 305, preventing the heads from properly seating and aligning with the block. You would need to modify the engine block significantly, which is generally not practical or cost-effective.