AD domain migration saving ACLs on Isilon

We have an Isilon cluster joined to our departmental AD domain. We want to start using AD domain of the central IT dept of our University which won't trust our departmental domain. The only thing common between the two domains is that 90% of users on our domain have the same user names on the central domain. We have about 1000 users, 100 groups, who own 3 PB of data in a few million folders. We can not risk up existing permissions on Isilon. What will be the safest way to do the domain migration?

Thank you,

Vinod