The privileged information can be redacted from the bills, but an explanation for its exemption from disclosure under the Open Public Records Act (OPRA) must be given. An unexplained claim of "attorney-client privilege" alone may not be enough. Of course, the challenge is to give a sufficient explanation to support the claim of privilege without revealing your client's privileged information.
This is a common problem, and many attorneys are switching to billing that contains no confidential information. After all, the bill detail is for the benefit of the client, and the client can always view the information in their file that is totally covered by attorney-client privilege to learn the confidential details of their legal representation. Put in the billing records only the information needed to justify the billing and maintain a separate file memoranda which can contain the privileged information.