Channel Balance Stamped 27 14L?

Confirm that the metal channel, not including the nylon fittings, is 28" long. If so, this is either an S351-28 or S390-28. The only difference between these two balances is the depth of the bottom nylon shoe, which can be thought of as the 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. 

You'll then need to pick a stamp option, which reflects the weight the balance is calibrated to support. That stamp option of 27 14L is pretty unusual. It would be best to obtain the exact weight of the window sash that these balances support. On the shop page for every balance on our website there's a chart that lists the weight range for each stamp option listed. You can then see if the exact weight of your sash falls into any of those weight ranges.