I need to get up there and measure it!I was told 7.5" is really what you need to put a 6" insulated liner in the chimney. If you have a 8x8 clay liner then you really only have 7x7 inches of space as the "8x8" liner is an outside dimension and the walls are about 1/2-5/8" thick.
The king requires 8" (round) flue so if you were doing an insulated liner you need 9.5" of space.