Numbers on the ballast are 20 4 JW CMC 7 I cant take pics of the installed ones

If the metal bar is 21" long, direct your attention to the S395-21 balance. You'd want to consider a 2040 "option," for a window sash weighing 15 to 23 pounds. Weigh the sash to be sure, though. The weight may be something different, in which case you'd consult the chart in the S395-21 product description.