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You may already know about the Miami Valley Genealogical Index, but I have just discovered it. There is Benjamin and George Olinger info, although I can't tell you if they are the "right" ones. It is at http://www.pcdl.lib.oh.us/miami/miami.htm. In general, it's a pretty awesome list.
I am interested in your McGee info. I have a g-g-grandpa, Font R. McGee, born Indiana 1868 (1866? I'm going from memory), in 1870 living in Shelby(ville) Indiana, by 1880 living in Dayton OH with his widowed mother and siblings. Font's father was Charles McGee, born 1830 in either Ohio or Dublin Ireland (depending what sources you trust) and living much of 1830 - 1863 or so in the Piqua OH area. Font's mother was Matilda, a 2nd wife, widowed in 1877.