These are 853 castings. Cartek did the 2xx on these. They have the 243 size valves ,cnc'd ,milled .030. Come with rockers and stands.no valve springs. Car made 420hp with just a 224/228 came thru a stalled auto so in a m6 should see 440/450 hp easy. Thanks for looking and happy bidding. If buy it now is used I'll include the 660 lift dual valve springs installed. Will pull them off if it doesn't hit $850.