You don't really want to know how heavy those cast iron parts weigh! And, yes they are sealed in those sockets with lead, which is melted and poured in.

To remove the sections: rent a cast-iron pipe cutter. You can hit them with a hammer and cold chisel (WEAR SAFETY GLASSES AND HEAVY CLOTHING!!!!!) and they will shatter. But you also stand the chance of loosening other sections.

Then, assuming you can use plastic piping, you can buy a rubber gasket that will fit into the socket and grip the plastic. (You will have to make sure that it properly seals against your cast iron pipe.) This is your adaptor. Use standard plastic fittings elsewhere. Don't forget to support the plastic pipe; while the rubber part may seal, it will not keep it from moving.

You can also buy a pour-in non-metallic replacement for the lead in the bell. If you do, ask how to seal the bottom to keep the stuff from dripping down.

CAUTION!!!
Before you begin touching the pipe, open up the cleanout at the bottom of the pipe and stuff a large towel inside (leave a little hanging out to remind yourself that it is there). Send the family away so nobody flushes while this cleanout is open- "I forgot, Dad". These pipes do rust on the inside and when you begin working with it all of the loose pieces begin to fall. I learned the hard way on a very old house and the whole drain system became clogged with all of the debris. When you finish, check to see how much is on the towel and scoop it away.

In a pinch I have cut them with a Sawzall and used little wedges to keep the weight off of the blade. It is heavy metal. Have you considered moving the doorway?
Best of luck!!!!

Thanks, guys. I decided to leave well enough alone.

See if you can picture this. The room behind the closet is about 10’ wide, flanked on each side by dormers, which form the sidewalls. Its depth is about 14’, but is not all usable because of the 7/12 sloped roof, which is only 6’ high when you enter, and slopes down from there. The entrance is actually in the best location.

However, in the middle of this area are these vent pipes, two sets joining into one about 2’ up. The main stack is the 4” variety, while there is an offshoot comprised of length’s of 1 ½” (or so) galvanized pipe and one 45 degree threaded elbow. The whole thing looks like a big, inverted “Y”.

My intentions were to remove the pipes where it comes out of the floor and where it comes down along the ceiling. Then, I would add enough plastic vent pipe so as to route it behind the hip-wall I’m building. Believe me, this would be a very straightforward procedure, and if not for the pipes being in iron, the project would already be a done deal. But the iron pipes sound somewhat difficult to move, and the extra usable floor space is probably not worth it.

This past weekend I laid down the floor. I simply worked around the pipes. When complete, the little room will be somewhat ”L” shaped, with only a small section of the 2” pipe actually in the room. The rest will be accessible from the remaining attic space, through a new trap door.

Again, thanks for all the input.