DC10's with General Electric CF6 engines did not have the waisted look to the No. 2 inlet duct. Northwest and JAL wanted Pratt and Whitney engines on their DC10's which had a larger fan diameter so Douglas fitted a larger inlet duct with the waisted (area ruled) look. The MD11 had larger engines than the DC10 so the larger waisted duct from the PW powered DC10 was used on all MD11's.
The 4 large banjo structural fittings that carried the tail loads were designed with this in mind and the GE powered DC10 had a smaller diameter duct lining passing through the banjo fittings. With the PW powered DC10 and all MD11's the duct lining was roughly the same diameter as the hole through the banjo's.