Ported cylinder heads will always produce better torque and horsepower than heads that are "as cast".  For any motor, these are a terrific upgrade over stock.  Valves are 40mm x 35.5mm.   The round ports on the Stage 1 heads produce great torque and low-end power, and the improved port and chamber designed will produce better drivability up to about 5500 RPM's with the right carburetor combo.  They're great for small displacement motors with mild to mid-range cams, terrific for buses and heavy vehicles, and will work much better than stock or big valve heads for larger displacement engines.  They come with stainless valves, hardened keepers and retainers, and dual valve springs.  Each set is custom-made to your specifications, so expect about a 2-3 week lead time.