As for them worn out used heads . I check them first before I spend hours porting them . And yes I have bought good used Dart -World heads . And I do have Friends that run real good times at the track with stock castings heads . One guy that I now has a 1969 Nova Home built 427 BB Chevy with GM iron heads . Every weekend he drives it to the track over 50 miles one way on the high way . Bolts on a pair of slicks runs 10s and he is a points leader . Put the street tires on. And drives it home . 90% of the heads I ported the guides were ok and the seat were not pounded . Even the new heads get the hand Lapping done to the valves before I assemble them . If I had to wait to buy a high cost set of heads they would be a bare set . And I would be the guy to put them together . COOL