1970-1974 andersen window balancer replacement

I need a replacement for this broken balancer. Beside the A/W manufacturer logo there are stamped this set of letters and numbers: B 4 19 7 70
No stickers or labels on window's frame to identify precisely type or year of manufacture.Double hang window, lower section clear glass approx. w=24"-7/16
H=13"-3/4, upper section the same. The approximate weight of the upper end lower widow pans is 7-8 lbs each. Any help on choosing a proper balancer replacement will be appreciated. Thank You very much, Bob.