Channel Balance Top and bottom identification

The channel balance is 28-5/5" long, width 9/16", depth 11/16". The sash weight is 21.2 lb.

The balance is marked 28 C along it's length and BSI across as in the picture.

Please advise what channel balance is suitable for these windows. Also, please indicate what the top and bottoms are.

The windows are non tilt approx. 36" x 64". There are no markings on the window itself, but will you be able to know the manufacturer from the channel balance marking?

Thanks,
Satish

The previous channel balance bottom was broken. Here is a new picture.