Need replacement

If the metal channel itself is exactly 23" long, then this appears to either be a S380-23 or S385-23. The only difference between these two balances is the depth of the bottom nylon shoe, so compare both with your old hardware to see what matches best. 

You will need to pick a stamp option. In lieu of having an old stamp code to go off of, yes, you'll need the exact weight of the window sash. You can then match that exact weight with the correct stamp option via the chart on the shop page.