Looking for a replacement

Hey there. This looks like an older version of the Series 140 Coil Balance system. That stamp likely means you need an S140-09 9 pound spring system. You can weigh the sash to confirm this. See the video below.

Start by looking at the 26-454 Pivot Bar, which is commonly seen with the Series 140. It only has one 'horn' on its tip, but that shouldn't matter so long as the hole spacing matches up. Please compare.

Dimensions for 26-454