help!can i use existing fireplace for ventfree gas logs?

i have a masonry fireplace in my 1895 home.here is the problem:i converted the attic into finished living space,thus having to remove the chimney to the fireplace located on the first floor.the ceiling in the room with the fireplace is 10' and the throat of the chimney is 42" off the floor.the interior dimensions of the fireplace seem fine.my question is,can i seal the throat of the chimney and use these vent free logs,and with what?i was considering a metal plate and fireproof caulk,but i am worried about the heat continuing up to the finished attic floor-i guess about 6.5 feet up.any feedback on this is appreciated!