Ok I just realized Estes has two different rockets named Polaris. The information you have given me is for the older Polaris model. I am looking for information on the newer one. I'm not sure when exactly it was released but I think it was around 2001. It looks very similar to the Guardian.
Here is what you need to do, measure the length of the nose cone and transition that you have.
The forward BT50 tube that the canards glue onto is 2.75" long. So add up the length of nose cone, transition and BT50 tube then subtract from 18.75" and that will give you an accurate length for the main BT55 airframe.