Replacement of 28 inch window balance on both sides of a double hung window

A quick learner from Ashland, Virginia says:
March 15, 2017
please direct me as to the correct widow balance replacement hardware that I should order from you to repair my double hung window.
The window is fine, just needs a new 28 inch window balance on both sides. If you can provide installation instructions it would be greatly appreciated. Thank you for your direction and assistance with ordering the correct parts to complete this repair. Please see attached photos.

The AAMA tag shows the manufactures code is ELL-1, series 400/500 DH

Best Regards
Mike
Channel balance
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Casey from SWISCO responded:
March 21, 2017
Hi Mike, This looks like our Series 770 balance system, compare and let us know if it differs. Looking at the stamp 27B, this normally measures 27", so be sure to double check the length before ordering!
27" Series 770 Balance
27" Series 770 Balance
S770-27
$12.70
How to replace a tilt-window channel balance.
How to replace a tilt-window channel balance.
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