Identify bbc head

[bert powell]

I have a set of super stock bbc heads, casting number 292/241. Was told they were done by Conway Witten years ago. They have a big X cast on the ends and was told their was something special about them. Anyone know? I have attached some pictures. I would like to have someone look at these to see about updating them, who do you recommend to update big block chevy heads? Thanks!