Need to replace channel balances on several windows

To start, you should ignore the stamp on the side. It is not a part number. What you're showing us is a 1/2" channel balance, Series 380 or Series 385, but I can't tell which, because the difference is based on size. Measure your bottom attachment as shown below. Choose Series 380 for a 1" shoe, and choose Series 385 for a 1-3/32" shoe.

Once you have the Series pinned down, choose a length. I doubt that any part of your balance measures 27". I suspect that the metal bar will measure 28", though, and if that's the case, you'd choose S380-28 or S385-28.

The final step is to choose a weight option. The "27 4" sometimes is related to SWISCO's 2740 stamp option, but not always. The only way to be sure is to weigh the window sash. 2740 holds window sashes between 19 and 26 pounds. If your sash weighs within that range, use that option. If not, check for a different option using the chart in the product description for the balance you choose.