I did see Langdon is mostly stopping with the 250's for some reason, unless I am misunderstanding.
But on 12bolt, They do have the split headers/manifolds.
I seen that one guy on 12bolt, I subscribe to his channel on youtube. I think its the one with the older El Camino. He did a good job, that thing hauls the mail! That 12bolt sight has the lump port too, I am not brave enough to try that. He also did a dyno on a 292 I think, and grabbed almost 400hp. That guys good, great personality too!