Hello there. The Series 385 does look likely. The only other possibility is the Series 380, which is very similar, except the 'depth' of that bottom nylon shoe differs. See the diagram below for an explanation. Measure the depth of your old balance's shoe to confirm which Series you should select.
For the length, measure the length of the metal channel, but do not include the end attachments in the measurement. Finally, regarding the stamp option, there should be a stamp on the metal channel that indicates this. If there is none, or you're uncertain, weigh the window sash that these balances support. Under the product description of every channel balance's shop page, there is a chart that shows what stamp option to pick based on the exact weight range your window sash falls within. Let me know if you have further questions.
