I would not use the 305 H.O. heads, they have extremely small chamber causing a insanily high compression ratio unless you use piston with huge dish in them. The 305 head and very small valve and poor port design. I would look at using Vortec 5.7 heads, they way out flow most of the "high performance camel hump" heads, and they are very reasonable in price (cheaper than rebuilding those crappy 305 heads). Check with GM Performance Parts.