At Least We Know the DHL Inlet is ROUND
This is from www.Airliners.Net
and all three inlets are round. I found this under "Boeing 727" A search under "Boeing 727-100" shows aircraft with round inletsand many of the aircraft in the 727-200 search results have round inlets. That is not conclusive, however, because in at least one instance I have found the same plane in all three sets of search results.
However, I recall when the 727 first fcame to Buffalo, NY and it seems as if the center engine did have an oval inlet. I think the engines have all been upgraded since for noise reduction as well as efficiency reasons and the newer ones require increased airflow, hence larger inlets.
As a bit of trivia, the 727's came to Buffalo before the 707's did because the runways weren't long [or strong] enough for the 707's.