Need parts for old aluminum windows

A quick learner from Pensacola FL says:
The overall length 30" X 1/2" width on the balancers, the markings are 2840 followed by a backwards D,and "B.S.I". the plastic guide parts are all missing, I have no examples of what is needed to get these windows working. Any help would be appreciated...

The home was built in the late 80s and is located in Jacksonville FL
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Hey, thanks for posting. This part is known as a channel balance, though I don't know exactly what you have. I've narrowed this down to two possible channel balance Series: either our Series 351 or our Series 390. Take a look at them now, then come back and read the rest.

As you can see, the only difference between these two Series is their bottom shoe. The Series 351 uses the 15-002 while the Series 390 uses the 15-001. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.
Comparison of <a href='Channel-Balance-Shoe/pd/Replacement-Sash-Support-Channel-Balance-Shoes/15-001'>15-001</a> & 15-002
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