Channel balance
Hey there. Can you show me the top fitting also? We need to see both for identification. Please confirm the metal channel, not including the end attachments, is 27" long. Finally, please show us any stamp on the metal channel. We should be able to narrow it down from there.
Thanks for your new photos. Based on what I see here, you have either our S380-27, S385-27, or S378-27 depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match.
If the old stamp is not present, or at least too faded to read, then your only other recourse is to weigh the sash on a scale. Any common bathroom scale will do. All of our balance store pages have a weight chart that indicate exactly how much weight each balance supports.