Sash Spring Replacement

I’m a handyman based in Nashville, Tennessee and I recently did a walk-through a customer’s house and they mentioned that one of their windows was not staying open. I had tilted the window off and determined that one of the spiral balance springs was broken.
 
I didn’t have a weight scale with me when I was at the house so here is the information I currently have, and I’m needing your guises guidance as to what colored tip/weight rating to buy
 
Sash length: 29” (just the tube)
Sash diameter: 3/8
Tip color: white
Window dimensions: 34.5” x 30”
There is no model or product information on the spiral balance, I doubt that it is a Swissco product. I’m planning to buy a pair of Swisco spiral balances and just replace the existing ones
 
I’m looking to replace both of the spiral balances, I went to your guys website and found the 900 Series 29” spiral balance (S900-29).
 
I believe this window is a double pane from my memory, so I’m assuming it’s on the heavier side. I do remember it being very heavy to handle and tilt off the window frame, so I’m gonna assume that it’s more in the yellow tip weight range (24-36lbs) 

 
The diameter of the tube housing is 7/16 (or closer to 3/8). The dimensions of the pivot shoe is: 2” x 1” (or 1 & 15/16 x 15/16 to be exact)

 
I just wanted to get your guys’s advice and opinion on what to consider and what I should buy. I unfortunately can’t easily go back to this house and weigh the window, so I’m just gonna have to do my best guess.