Replacement Balancers for Alenco Windows

Hi, 
I need to locate the correct balancer for an Alenco window (vintage year 2000). The old balancers are 28" in length and the sash weighs 31.5 pounds. I think I need the Swisco S350-28 2760. The old balancers are stamped with a number of "2790 31". I'm going to attempt to replace the balancers on one window first and then will likely have to go through this process for at least 10 more windows once I feel comfortable with the process. Please let me know if my assumption on the Swisco model number is correct or if you have some other guidance. Thank you!