Spiral balancers for 30 year old aluminum Milgard dual-glazed windows

A handy person from Sebastopol, CA says:
I've got multiple single-hung aluminum milgard windows that are about 30 years old, and believe I've found the correct replacement components on your site, but would like to be sure, and would also like to know if you can custom assemble the shoe onto the spiral balancer for me.

It's a 3/8" spiral balancer that's 30" long and is holding a window that weighs 12.2lbs. That seems to indicate a 30" S900 red-tip balancer.
The shoe looks to be special attachment 15-142, which matches the measurements on your site (picture attached) at 1/4" wide x 1" long.

Please let me know if this is correct, if you can rivet the shoe on for me, and how to go about ordering. Thanks!
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Hello! You're definitely on the right track, though we would use our Series 306 balance to make this. The end of the spiral extension has a little more room than the Series 900 does, which will allow the 15-142 to install comfortably. I would be happy to set up a custom order link for you. Can you just tell me how many you need?
A handy person from Sebastopol, CA says:
Hi Tom,

Great, thanks. Yes please set up a custom order link; I'll need a total of 4 of these.
Profile picture of Tom
Tom from SWISCO responded:
Perfect, thanks. I've emailed you a custom balance order link, which you should receive soon.
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