I need balances for 25= year old Alenco window. The channel is 22 inches long, 9/16 wide and 5/8 deep. It has "21 C" stamped on the channel. I replaced a longer version of this one a few years ago that is a little less than 28 inches in length. It has the number 2720 stamped on it and was purchased directly from Alenco. I am not sure of the series I need from your product line.