Only hard part about the whole job will be soldering a cap on the old line.
There may be a simpler way to do this.
We still have not seen a picture yet so this is just a guess.
You could cut the pipe and just slide on of these on the same pipe.
No soldering or tools other then the pipe cutter needed.
I would use a stainless steel braded supply line made just for dishwashers to make the connection.