Need 4 channel balance

I have two windows that need the balances replaced. The house was built in 1966 and they are probably original equipment. The balances do not have any part numbers or manufacturer. The balances are 18 and 3/8 inches not counting the plastic clip on the end. Counting the end pieces they are 18 and 7/8 inches. The window frames are aluminum. The frames do not have the window removal clips shown in the internet videos.There is a rubber dam at the top and under the rubber dam is a clip that holds the top of the balance. When you remove the dam you can raise the window all the way to the top and the window will come out of the track. See the pictures for the parts needed.