Vintage window balances

Hi, we have double hung wood windows in a 1950s ranch. No identifying marks that I can find. The balances seem to be just a plastic tube with a spring inside, screwed to the sash at the top and the bottom of the window itself. We would like to replace them with something better, if possible. What kind of modern balance can we use, and how can we determine the dimensions and models we need? There are a few different sizes of windows in the house, but they are all constructed this way.

Bonus question: if we want to open both the top and bottom windows for better air flow, how can we install screens for both ends? (These are not removable tilt out windows.) The sash has channels for upper and lower storm windows, but only one for a screen. Do you double them up somehow, or do you replace one of the storm windows with a screen in warm weather?

Thank you!

Thank you so much for your reply! How does one weigh these? I cannot discern any means to remove the sash from the window short of dismantling the actual jambs. Is there a way to approximate?

Thank you! I will hopefully be ordering soon!