Balance spring

Unfortunately, it's not possible to identify a balance based on the stamp alone. That only tells me how strong the spring is. 

In order to properly ID the right balance for this application, I need you to remove an undamaged version from the window and show me a clear shot of the top end, bottom end, and the shoe or clip at the end of the cord.

Removal prior to identification is necessary for this kind of balance. There's no way to avoid that.

The shoe being damaged is unfortunately going to prevent us from accurately identifying this. These knife lock shoes come in a lot of varieties, with some being obsolete, so the precise design of this part will be the major determining factor as to whether or not we can help. Seeing this in undamaged condition is essential. At the very least, I'd like to see the broken pieces put together to resemble its original shape.