Channel Balances

I am trying to replace channel balances in my circa 2002 Kinko windows (non-tilting)

Series 380 looks like my balance with wings on each end I assume to keep 1/2" channels centered in track. My old balances are stamped 29 6 (or 29 4 or 29 3) and are 30" long (metal channel only not counting plastic end pieces. Am I correct that I need Series 380 2960, 2940 and 2930 to replace? Thanks for any help.