1620 is stamped on front side of channel.

Hello,

You very well could need the S390-17 as long as your bottom attachment has the same 1-1/8" depth as shown below. If not, I'd recommend you take a look at our S351-17 with a 1" bottom attachment. For wither balance, you'll need a 1620 spring strength option for your replacement based on your balance stamp. Thank you!