The floor bolts on my toilet were rusted and broken which made the toilet wobbled. I removed the toilet to install new bolts. But, the floor flange on the drainage was also rusted and broken. It seems that this old iron flange is fused with the floor as well as drainage pipe below. My house is at least 40-50 yrs old.

I got the new PVC flange that is suppose to be the "replacement" for old cast iron flange. But the pipe extension below the replacement flange is too big for the drainage opening in the floor. Should I, remove this old iron flange or put more flatter metal flange on top of the old one.

What's the easiest way of removing the old one without damaging and plumbing system or the flooring. And,

If I go with putting the new metal flang on top how would I secure it in place on the old one

Please advice,, thanks

Let1s start at the beging. First I hope you are on a convenal floor. (not a concrete slab) You will have to get under the house and cut the cast iron pipe off. Ihope you have room to if not you may have to dig out from around the pipe so you can. There are ways to cut the cast iron pipe, #1- they have a chain type cutter. #2- You can use a carbide saw blade on a skill saw( have to be real careful this way) made for cutting metal , includeing cast iron. #3 use a sawzall with a metal cutting blade. You can start with a short one until you get cut through. Now remove the pipi and old flange from inside bathroom , measure from top edge of pipe to inside of flange up to where a slight bevel is inside flange deduct about 1/2 " flange has to be down on floor then cut pipi 3 or 4" pvc sch 40 put a rubber boot fromyour castiron pipe down to the 3 or 4 " pvc ( the rubber boot is one piece) Loosen clamps slide boot down on cast iron.( put vaseleen) on pipe Drop flange and pvc glued already set and screw flange down in right possion for setting toilet on use vasleen on pvc pipe slide boot up on pvc half way. tighten down the clamps .::" Ithink you can finish from here . Hope I1ve been of help If you are on a concrete slab ,do the same way but a lot harder.;'

Getting under the floor in the basement and cutting cast iron pipe is going to be very tough because of the access, impossible if I DIY... may be a proffessional plumber would be able to do that.
Anyway, I am not able to tell if there is a separate flange attached to the pipe at it's opening in the floor or is it just one piece with flange shape on top with slots for bolts on it. Is there a more easy solution to this . I am trying to brake the flange shape opening and make it more flatter so that I can put a new flange on it.

Is there a way to find out if there is a flange on top of drainage pipe or not and separate it by braking it or something.

[B]Is flange bolt{S} only broken?
Or is the inside of flange going to drain also broke?
If flange bolts only----- they have repair flange kits,no remaval of old required/B]

The easiest way to just put 3/8 wood screw (if its wood floor in good condition) or to drill a hole in concrete, put 3/8 anchor with screw. Assuming that flange round is in condition that it still can be holding wax ring in level, round shape