Here is the AA policy that protects passengers on separate tickets:
https://ssc.aa.com/prmportal_enu/Age...ng%20Index.pdf
See page 13 for specifics. No mention of MCT in the policy document, but I'd definitely make sure that I satisfied the MCT. Dunno if 60 min for AA D to D at ATL satisfies the MCT, but I assume it would.
I would book the 7:03 flight to ORD. 60 minutes is plenty of time.