I might set up some plastic to catch any sparks. Use a small 4 or 5 inch grinder With a narrow disk. As you can work it at floor level. Stuff something in the pipe to catch any pieces you may drop in there.


The flange kit you show is not a bad ideal. As long as the Od is smaller than the id of the cast pipe. As it gets close to the flange. Although it has the rubber to prevent sewer gas from getting in the house at the lowere end I see. . So I suspect it is purpose designed.


Of course check for wood rot in the area you have to screw the flange down. Again as long as the neck is the same diameter and I suspect it will be as the cast pipe. Near the flange all should go well. You do want to feel a friction fit when it slides in the cast iron as well. If not remove the rubber and build up some level of plastic tape under the rubber to make it so. Once again though being purpose designed I suspect no issue. With sewer gas.

Now I do not know how off level the floor is. Front to back or side to side or both. I would measure the base of the toilet and use a level to figure if I need to do anything else before starting. I would not want the flange badly tilted. Actually what you are proposing is what a professional would probably do in your case anyways.

I always use the wax seal that incorporates a plastic extension into the drain. They are very common. If they make a difference or not I have no ideal. They cost about the same so why not? Also do not get too aggressive when tightening down the toilets securing hardware. That plastic flange may not be the strongest. Sometimes I tighten down and let the seal squeeze out a little before tightening down more.

I leave you with remember I am not a professional in this area.

You do want the flange bottom on top of the floor. Not recessed into the floor. I just re read you post.