Window Channel Balance

Hi - I'm looking to replace some old channel balances for a window in my home. I need help selecting the correct parts. It is a non-tilting window; the metal channel is 30" long, 9/16" wide, 5/8" deep. They are marked "29 3 IP Caldwell" I know that the plastic bits at the end vary - I've attached pictures that show the marking and each end of the channel balance. Please let me know what the correct replacement style would be. Thanks!