Balance for old wood window

I need help identifying the balance/parts for my old wood windows. The windows are approximately 55" L x 32" W and are in an old brownstone in NYC. It may not be visible here but the number on the metal shaft looks like a 2 4__ __ . The last two numbers or letters are illegible. Then beside that code is what looks like an EO. Unfortunately I have no other information. Thanks in advance for any help you can give!
Rosalie



Hello,
We can't be sure with your balance assembly still installed but what I can make out resembles the S751 channel balance. You'll need to remove the assembly to confirm the specifications of the knife lock shoe match and that your assembly has the same ribbed channel. You'll also need to confirm the length of the metal channel as shown below.


As for the stamp code, I'd recommend checking the balance on the other side to see if it is easier to read. If not, you'll need to weigh your sash to determine which strength option you'll need. There is a chart on the product page that explains how to choose your option based on the sash weight. Thank you!