Hello, thank you for posting,
Your channel balance resembles the Series 377. Please review to confirm that the attachments match. Even though the stamped numbers are different, based on these numbers all the metal channels excluding the nylon attachments should measure 29 inches long.
The number stamped on the balance indicates the strength of the spring needed to support the sash. The number should be the same on both sides per window. The numbers being different indicate that the sashes are different weights. Please review the stamp option chart on the product page for comparison. Let me know if you have any additional questions!
