Really, you should bring the old DS to the shop and let them do all of the measuring. Without doing that, you are asking for major problems. It might be a pain initially, but it will ensure the best possible outcome.
My DS place had a new one ready for pickup in less than 12 hours. No joke.
Also, if you climb under the car, you'll see that the OEM one barely bends at all. The middle joint it there for reduction of harmonics really. The length difference between a single piece and OEM is negligible.