Channel Balance question

The Series 350 only has wings, or 'side tabs', on the bottom nylon fitting. Both of your balance's fittings have wings; therefore, you actually need either the S380-26 or S385-26. The only difference between these two balances is the depth of their bottom nylon shoe, or the shoe's 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. See the illustration below for reference. You are correct, the stamp 25-3 means you should select a stamp option of 2530. 

Comparison of the S378, S380 and S385 balance shoes.