I believe the procedure should the same for Windows 8 if you want to give that a try. I use this PE with my Win7 clients now too since it already has all the drivers I need. The only issue I've had was my machines weren't being added to the domain after cloning so I had to do an additional configuration task. If I remember corrrectly, that only happened when I was using WinPE 3.0 (Win 7) and hasn't been an issue since going to WinPE 5.0 (Win 8.1).
Also, simply removing the unattend step...
{
what = unattend,
path = "{manifest}\\ghost\\unattend.xml"
}
from manifest.txt in the GSS WinPE 2.0 PreOS's you are using for Windows 7 should allow them to work on Windows 8 clients.