I have determined that the channel balance I need is a 27" series 380, however, I am not sure which stamp option I need, as there is nothing visible on them. They are the kinco series mark 40/50 HP. H-LC50-53x77. Thanks for your help.
Tom from SWISCO responded:
May 9, 2017
If your balances have no stamp on them, you will need to weigh your sash and refer to the chart on our S380-27 store page. That is the only other way to determine what option will work.