You cannot attach a plastic flange to cast-iron without having a leak. A new flange can be installed on top of the floor very easily. You do not want the flooring to butt up against the toilet, since any replacement toilet will not fit the recess and then you would still have to raise the flange, besides patching the flooring to fill the void.: My cast iron flange has a piece missing where the bolt fits. I also need a flange adapter, : because the floor is too high. Can the luann and linoleum butt up against the toilet instead of going under it? There doesnt seem to be a way to attach the pvc riser I have to the iron flange unless we drill holes into the flange : and it might crack or break somehow.