The Lusmagh RC records start around 1832/1833 but when I search the subscription site Roots Ireland for all of Co. Offaly, I did not locate a Michael Killeen marriage to a Margaret Doughney. Maybe they married in England?
The 1853 Griffiths Valuation head of household listing for Lusmagh civil parish does show a number of Killeens in the parish including five Michael Killeen records. There is no way to determine if your Michael Killeen was one of the five listed.
Have you considered a DNA test? Possibly you will have matches with individuals who have Killeen connections.