Okay, to answer my own question:
https://musicbrainz.org/ws/2/discid/I5l9cCSFccLKFEKS.7wqSZAo...
will give you a list of "releases" for that discid. Use the release ID in this endpoint, with the included parameters:
https://musicbrainz.org/ws/2/release/8e061dc4-790e-4587-ba53...
and you'll get the track data. Not quite sure how to get the album art yet, but should follow.