Close comparison with earlier vinyl pressings reveals that in addition to Blonde On Blonde, two other Dylan albums were remixed for their initial 1987 release on CD: Bringing It All Back Home and John Wesley Harding. Notes relating to the remixing of the latter have surfaced, as shown below. The intended CD is identified by its already-allocated catalogue number, CK-9604, and the source is indicated as an 8-track reel. The handwriting has been identified as engineer Tim Geelan's, and the notes as pertaining to a digital work reel. See this page on audio engineer Steve Hoffman's Music Forum. According to Hoffman himself, at this time digital mixing would have been performed on a Sony PCM-1630 16-bit system - see this post on the same forum thread.
What this means is that the 1987 CDs of Bringing It All Back Home and Blonde On Blonde would almost certainly have likewise been 16-bit digital remixes prepared by Tim Geelan.