Chimney rebuild from roofline up. ‘75 VC Defiant in an 1170sqft house. Oversized. Flue tile is 7x10 with a corrugated steel liner. Replacing defiant with something new that fits the house. 6” insulated liner but won’t fit w/in the tile. 2 options custum 4.5x7 insulated or 6” insulated and bust the tiles out. Top tile at very least is already cracked. Easiest install is bust out? Secondarily, bust out only to below thimble? And if thats the case should liner T and cap terminate just past remaining tile so no ash ends up behind remaining tiles?