Sun Air window Balance replacement

A handy person from CA says:
I have a Sunair window Balance w/2740 B.S.I stamped on it. I am a bit confused as to which series to get 350, 380 they all seem to have the same specs and end pieces. Thank you.
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Donna from SWISCO responded:
Good Afternoon,

A lot of the channel balance series do look very similar but there are differences between the balance attachments. The balance attachments are the plastic (sometimes other materials) attachments found on the bottom and top of the channel balance. If you need help choosing the replacement channel balance series that matches your existing balance, please submit a couple pictures of your channel balance's attachments. We can help you choose the proper balances series based on your pictures.
A handy person says:
I have attached the photos.

User submitted photo of channel balance attachments.
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Mike from SWISCO responded:
Does your bottom shoe have wings like the 15-005 shoe or does it look more like the 15-002?
A handy person from ca says:
It has wings like the 15-005
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Mike from SWISCO responded:
Can you confirm the length of the channel portion of your balance? I think it may be 28" in length.
A handy person from ca says:
Yes, It is 28" in. long
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Mike from SWISCO responded:
This appears to be the S350-28 Channel Balance with the stamp option 2740.
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