unknown window balance

A quick learner from Naples, Florida says:
I ordered some replacement window balance springs from you a while back and repaired some of my windows. Now I'm trying to help a neighbor but he has different windows and different balances, and I can't find a reference to the parts. The two photos above are the top and bottom ends. The only identification on the channel is US 27E. The measurement of the channel end to end is 28". It is 1/2" deep and 5/8" wide. Any help you can provide is appreciated.
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Bob from SWISCO responded:

Thanks for writing in. This channel balance looks like it might be our S770-28. Your stamp code is from an older rating system for this balance; the safest thing to do would be to weigh your window sash. You can then match that exact weight with one of the weight ranges listed alongside each stamp option on the product page. If you need to replace the pivot shoe, please give us the width and thickness of the shoe, and we'll try and find the proper match. Many thanks.

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