Matching window balances

Hello, 
 
I always seem to miss your open hours for a live chat as I am on the West Coast, so thought I would write a message instead.
 
I have two separate windows in an older house (ca. 100 year old craftsman style) in Seattle that are having problems with failing window balances, but I am pretty sure these are neither “original equipment”
 
Window 1: Bathroom
A tilt-out window with coil balances.
Coils are NOT marked in any way that I have been able to detect. 
 
From your website, they do appear to be Series 190 coil springs, but I cannot determine the correct version.
One of the existing springs is badly kinked a few inches from the outer end, and I believe that this is probably the root cause of the sash not staying correctly adjusted, but slowly slipping downwards under its own weight.
 
Sash weighs 11.6 pounds. (27½” wide x 17½” high)
 
I could not identify an exact match for the spring shoe, but suspect it might be your 15-087, though that seems to be normally paired with S180 springs (2-holes?) whereas the current springs that I have are single hole. I don’t know the significance (or not) of this!
 
Given a sash weight of just a little under 12 pounds, should I normally use 2x S180-06, or get closer to the net weight albeit with a slight left-right imbalance, by using one S180-5 and one S180-6?
 
In any case, please can you confirm that the springs are just loosely inserted into the shoe, and then sandwiched between the two halves?  
 
 

BTW, though I annotated the image to show that the shoe depth is ½”, it is actually slightly more than this, as the springs themselves are exactly ½”, making the shoe depth closer to 9/16” due to the ‘sheave’ or cheek thickness of approx 1/32” (x2) 
 
I understand the advice to replace springs as pairs, but is there any practical necessity to replace the shoes at the same time?
 
Window 2: Bedroom 
Andersen Sash style
 
Here, rather annoyingly (having discovered the exorbitant cost of the Andersen balances!) the lower sash strings have worn through on both left and right sides.  
 
 

Even more frustrating, for now, I cannot find a match on your website based on any of the legible markings on the two balances I have now removed.
 
The top face (as installed)  has the generic 11600 (but -3 rather than -17) marking, and a couple of patent numbers 1967 CAN. and 3,335,455 
The bottom (as installed) side markings carry a legible 11600-17   
 
and on the opposite side a much less legible marking that could be 3E9 9 something-something (9/27?), then maybe 486.   
 

Anyway, if it helps, this sash weight is 16.8 pounds. and about 31½” wide by 27½” tall 
 
I look forward to receiving your advice on the appropriate replacements I need!