balancer replacing

This appears to be a Series 380 or Series 385 Channel Balance. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. You'll need to measure the length of the metal channel, not including the nylon fittings on each end, to know what length to select. Let me know if you need help choosing the stamp option. Finally, see the video on this page that shows how to install this type of balance. 

Comparison of the S378, S380 and S385 balance shoes.