coil spring replacement

Thanks for posting. Well done, I agree with your entire assessment. This looks like the 15-192 Certainteed shoe, which uses Series 170 Coil Balances. If there is a '5' or '405' stamp on the spring, then the S170-405 5 pound spring is what you need. The pivot bar also looks like an older version of the 26-175. All these parts should be in stock currently. Let us know if you have further questions. 

Coil balance systems are modular, meaning you only need to replace what's broken; so yes, if the old coil spring is not torn or worn, you should be able to reuse it. The 15-192 does not come with new fasteners; either reuse your old ones, or use the 33-072. Let me know if you have any other questions.