That is a little odd. With a stamp of 2220, the balance should only be 23" long. Are you making sure to only measure the metal channel? Part of me thinks it could have been cut down, but if it were then it would have originally been 24", which means the stamp would read 2320, not 2220.
Either way, the length does not tell me what Series you need. The only difference is the size of the shoe. You will need to measure yours and carefully compare it to the measurements we have on our site.