samba - Sep 2014 - Samba 3 PDC to WS2012 AD Migration

Hi,
I have quite a difficult task to solve.

I need to migrate from Samba 3 to WS2012 AD. I know the steps are Samba 3 to
Samba 4 to WS2008 to WS2012R2.

I managed to upgrade Samba 3 PDC to Samba 4 AD, but I am not able to move roles
to WS 2008 as I have some DNS related problems.

Is there any howto regarding Samba 4, DNS and Active Directory? Better I would
appreciate some lines describing the whole process of migration or someone who
has already done this.

Thank you very much.