I have purchased a Appalachian Trailmaster 4N1 Catalytic Stove. It is used I would say about 10-15 yrs old. It is in good shape however it needs a little TLC. ie. a new door gasket and some new bricks. I want to install it in a factory built fireplace and was wondering if I could use the existing 8"flue from the fireplace or do I have to line the existing flue with stainless or some other insert specific flue liner? My existing fireplace was installed in 1999 and the flue appears to go all the way to the top of the chimmney. Also, my fireplace needs about 2" more height but I think I can trim some height off the bottom as I have about 6" of open space between the unit and the top of the hearth. Is trimming not an option or okay? Also can I remove the faux brick panels on the sides and rear to accomodate installation. Any help would be appreciated. Thank you.