Becky. I agree with your initial assessment that the "oversight council" would focus on "technical and operational issues" (as opposed to policy issues); and therefore GAC participation in the council will not be required even though GAC participation at an equal footing will not be inconsistent with the multi-stakeholder model.
However, I think GAC participation in the council might be essential in the scenario where the oversight council decides to change the IANA operator in the future. If the council decides to contract a different operator (different from ICANN) in the future, would it not lead to various policy issues such as jurisdiction of the new IANA operator, financing of the new IANA operator etc - where the insight of the GAC may be beneficial?
Therefore I think GAC should be a part of the oversight council.
Regards,
Guru