As the data is on Centera it is not as easy as drag and drop follwoed by some SQL updates. You will not perform a migration. You could do this witht he built in Move Archive Tool, although it is not really built for mass migrations. There are everal third party products out there than can do this for you.
I am more than happy to have a call with you to discuss such a project.
There is no such documentation; each Enterprise Vault archived item corresponds to a SavesetID / TransactionID and each of them do have the corresponding centera CLIP-ID.
The unique way of migrating any EV archived data from Centera storage to Isilon (NTFS where each archived item is a .DVS, .DVSSP, .DVSSC or .CAB) would be moving the archives.
The native solution is Move Archive; I would recommend third parties solutions for migrating high volumes of data please refer to https://www.veritas.com/product/information-governance/enterprise-vault/archive-everything (content migration)