need help to identify which channel balance to buy

Thank you for the product description. If you could send us some photos of your balance removed from the window, we should be able to recommend a replacement. Please include both end attachments in your photos. Thank you. 

Thanks for the photos. Judging by the presence of wings on the top and bottom attachments, I see this is a Series 380 or Series 385 channel balance. I'm leaning heavily toward the Series 385, specifically S385-27. Measure as shown below. If you have the shoe in the photo, go with Series 385. You can take a look at the 2660 stamp option, which looks awfully similar to your "26 6" stamp. You'll need to pick an option in order to get the right weight and place your order.

Alternate view of 15-004