Is this window balance replacable?

You have a very old balance. They haven't made this design in a long time, but the good news is that we have a modern balance that can work in its place. See our Series 500, along with a 17-012 bracket (sold separately). You'll also need the 75-005 charging tool to install.

At this stage what we need to figure out now is what length and spring strength to go with. To determine these details, I need you to tell me the height of the visible glass and the weight of the sash. Please be as precise as possible.