Block and Tackle Replacement

A quick learner from Alabama says:
I'm assisting my father with finding a replacement block and tackle for a window he's installing. Unfortunately, the windows were out in the weather for quite a while so the springs have rusted and one broke. I have attached photos of the block and tackle that is not broken and the stamp on the side of it. The other photos are of the plastic piece in the channel of the window and the two ends of the block and tackle. The ends look nothing like what I've found online so I'm have a tough time. The string end is attached to the top of of the channel by a screw through the small metal plate.
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Tom from SWISCO responded:

Thank you for your patience in this matter. Looks like you need a new channel balance. See our S765-33 channel balance, this looks like a good match. You'll likely need our 32-5 stamp but you can always weigh your sash on a scale to confirm.

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