How far will the new sink location be from the galvanized stack? Local plumbing codes dictate the maximum allowable distance. I'm a little confused on your intentions. You may want to cap the existing drain at the floor level, and run a new drain line, then figure out how to use the existing 2" stack. Cutting 2 inch holes won't work, because the O.D. of the galvanized is 2 1/4". You would need a bit that's at least 2 1/2". Post back and let me know.