I purchased a slant head from rocksolid. I'm no expert, but it looks stock and untouched to me. I havn't needed to fit it, so no idea if its any good or not.
I read on their site that they run in the motors for about 500kms on a dyno. That might be worth something.
Good luck to them if people buy their product, but I got into this as a cheap hobby, that I can do the performace mods myself on.