CHANNEL BALANCE
If the metal channel, not including the nylon fittings on both ends, is 30" long, then see either our S380-30 or S385-30. The only difference between these two balances is the depth of the bottom nylon shoe, or 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. It's hard to read your old stamp code; I'd obtain the exact weight of the window sash. You can then match that exact weight with one of the weight ranges listed alongside each stamp option on the balance shop pages.
Hey there! Bob's not here today but I'll do my best to help.
I can't really make out your dimensions from these photos, but just eyeballing your hardware I think your balance may be a closer match to our Series 395. This has a 19-005 top and 15-001 bottom nylon fitting. As long as those match then you should be good to go!