UNIQUE 27-D-40 Channel Balance Questions

A home owner from Ocala, Florida says:
I have what I believe is a Series 770 which measures 28" long. The only stamp on it is UNIQUE 27-D-40. Should I choose option 28D when ordering? The window weighs 25 pounds.
Also, is it necessary to replace the pivot lock shoes? They appear to be OK, and I couldn't find one that looks like mine. Please take a look at the pics and help me order the right stuff. Thanks!
user submitted photo of channel balance and pivot shoe
Profile picture of Donna
Donna from SWISCO responded:

If pivot shoe is in working order, there is no need to replace.

28" Series 770 with 27D stamp will carry a window sash weight range of 23 through 28 pounds. This will work well for a 25 pound sash.

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
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