Old balances

I'm guessing these are about 30 yrs old (late 80's). They appear to be a match for the S800-24 (metal portion is 24" long); the only concern I have is the shoe, which doesn't look exactly the same (pretty close though). The only markings are "23 C" and something that looks like "3.S.I." (although the "3" is kind of sketchy).
Any help appreciated.

I spoke with someone on the phone yesterday (very helpful, btw!) about my 24" channel balances and the general consensus was that I need either the 390 series (with a 15-001 shoe) or the 351 series (with a 15-002 shoe). The 1/2" width is right, but as you can see from the attached, neither shoe is a perfect match. I THINK the 15-001 will work; I didn't see anything else on the website that looked any closer, but I just thought I'd run it by you to make sure I'm not missing something. Original inquiry/discussion with more photos was D102745. I guess it makes sense to order a single pair to test out, before ordering enough for the rest of the windows. Please let me know if I'm barking up the wrong tree. :)