window LR Channel Balance

Thanks for posting, and thanks for all the thorough information. If the metal channel, not including the nylon fittings, is 22" long, then I agree this could be an S390-22. The only other possibility is our S351-22. The depth of the bottom nylon shoe is the only difference between these two balances. Compare both with your old hardware to see what matches best. See the image below for reference.

You'll then have to choose a stamp option, which reflects the weight range the balance is calibrated to support. Your old balance's stamp is a bit unusual. Since you helpfully included the sash weight of 35.3 pounds though, we can tell you that you should choose a new stamp of 2170. This will support a window sash in the weight range of 34 through 37 pounds. 

Your Top Sash Guide resembles our 18-179. Please compare.