Will Vortec 350 heads work on vortec 305 engine without any machine work?
No, Vortec 350 heads will not work on a Vortec 305 engine without machine work. While they share the Vortec design, the bore spacing is different. The 350 has a larger bore spacing than the 305, meaning the head bolt holes won't line up. You'd need to have the heads machined to fit the 305 block, a significant undertaking.