The set of 440 source heads I bought ised needed valves and guides to be right. The press fir on the guides was scary and the valve stems measured like a fun house mirror. Figure you will have as much in the source heads as a set of trick flows to make them move air and not be a time bomb. My advice would be to by the source heads bare and do your own due diligence. 600hp n/a no problem. A good set of factory appearing aluminium heads would have decent resale value also if you upgraded at the next short block.