[Vwdiesel] cleaning cooling system on 1980 pickup

[Will Taygan]

Alright, I've got lots of oil in the coolant.  I'm pulling the head soon.  Any ideas on how to clean oil out of the cooling system?

Furthermore, I can get the manifold off, but I can't get the 6 nuts that hold the manifold to the downpipe off.   P'Blaster isn't enough(so far).   Does this need to come off for the head gasket or can I just push the manifold out?

Will Taygan
80 & 81 diesel pickup
Concrete, WA