cast iron under the sink

I have a 50 yr old house. I am replacing the sink. Under the counter is cast iron pipes coming into the house, iron j-trap and then connects to pvc to connect to the sink. This comes out to 14" from the wall. The new sink I bought, the holes are only 7" from the edge of the sink. There is a cast iron coupling right at the wall where the iron comes in and a 9" pipe between the wall and the iron j-trap. How can I shorten this to 7 or 8"? I don't do much plumbing. Is there a special tool to work with removing cast iron pipes? Or is it worth it? I'm thinking about just getting a different sink.

I usually cracked those (Durham), cast fittings, with a heavy short handled sledge and backed it up with an 18" pipe wrench. Or you can cut the steel pipe back near the wall and give yourself more room and transition with a no-hub band to pvc.