Les Schmader did a set for me, not C6s, but D2s, I run them on my 461 EFI truck motor. 490 HP with a 230/236 112 LSA cam. They flowed 277 cfm at .550, exhaust was way better than stock but nothing special
I would say if going with any of the more undesirable heads, you should only do so with a reason. In my case I had truck headers and didn't want to reflange or modify.
C6AE-R, much better head, they can do 15 cfm more reasonably and exhaust is much more capable than -J or -U,