I have never bought that all the vendors we see make the heads they sell. In fact I think they really are buying CNC heads GM or others makes and then add big price tags to sell them as if they made them.

GM makes two CNC heads for performance, the more aggressive 11.2:1 compression head (PN: 88958622), or the just released 10.5:1 compression heads (PN: 88958665).

The 8622 heads have a small 62-cc combustion chamber, while the 8665 heads have a close to the production 65-cc chamber. Both heads have 250-cc intake ports, 85-cc exhaust ports, and can support north of 500 HP !
They come with the LS6 factory valvetrain, hollow-stem stainless-steel valves (sodium and potassium filled on the exhaust side), chromimum-silicon (Cr-Si) ovate beehive valve springs.

So before blowing your money on some vendor selling who knows what I cannot see them beating the design of GM engineering for high performance heads.