461 and 461X heads 

Have a set of 461,462 and 186's

look in center intake ports on 461 you see where humps are in top runner for valvue cover bolts 461x didnt have hump

back when we were running a circle track street stock. we ran 461 heads that were professionally ported just so we could run up front. it was cheating yes. we got caught. then got some 461x heads went straight to winners circle. 461x was now an illegal head. total horseshit. I'm looking for some now for my wife's 68 Camaro.