I have now had the time to replace the balances on the window and all seems to be working just fine. The replacement balances do seem to be a bit heavier duty and stronger than the original balances, but the window does operate and remain open as expected.
Could you review the photos and just validate I have the correct spring strength? The window is 33W x 30H double pane. I do not have a scale to get the weight of the window.
29 4 is often correlated to SWISCO's 2940. If it holds the weight as well as the old balance did, you should be fine. If it doesn't, you may want to weigh the window. 2940 holds 23 to 28 pounds. Make sure that's what your window weighs.
As for the ends, as you noticed, I don't think they're different enough to cause a problem.
