They are 6X heads but can not make out -4 or -8 they are the stock heads off the 78 block. I have been doing a lot of reading and just ordered Jim Hands book. Really did not want to build up the #s matching motor to play with but if I can redo the 6X heads to drop comp to around 9 to 1 then I would feel better about it. Any help on picking parts based on exp would be great.