Replacement 27 4 Channel Balance

I have to applaud you. Perhaps one in a hundred customers manage to provide the right information to identify a channel balance all at once. There's almost always something missing, but you nailed it.

Your balance is the S350-28 with a 2730 stamp. Your existing 27 4 (2740) might just be a little too strong, or maybe the sash isn't exactly 18. If you're confident in the measurement, and it's below 19 pounds, go with 2730. If it happens to be above 19, go with the stronger 2740.