Window Balance 26-5 RE BSI N

Hello, I'm trying to ID a balance spring that is 27" in length with a stamp of 26-5 and a sash weight of 20#. Channel dimensions are 1/2" wide x 1/2" deep. Spring shoe is 1 3/16" wide and 1 7/8" long.

Also can you also provide guidance for sash removal and installation? I am unsure of window make but tilting sash in till perpidicular to frame and lifting or pulling on either side is ineffective. From what I have been able to determine it is a Norandex Extreme or Viewpoint or Prism

Thanks in advance for your assistance, David

I just ordered same! Thanks