Before you do anything, pull the heads, and check the water jackets. If it's raw water cooled the jackets might be so rottted that it won't pay to invest any kind of money in those heads. My heads(1988) were rotted around the water passages at the gasket surface opening the holes to the point that they were impinging on the combustion ring. Time for new heads. Cutting a 30 degree back cut on the valve face helps partial lift flow. It's good for a few CFM. Check out http://www.chevyhiperformance.com/te...518/index.html Good info on head porting for SBC.