Replacing old discontinued 7.737.877 Crossbow Balancers

Hi All,
I found your company and this discussion board after endless searching on the internet. I believe I already have identified the correct replacement but I am a bit ahead of my skiis as I have never done this sort of job before. I am a tinkerer and software engineer so I know I can figure it out but rather than aimlessly going about it through trial and error I figured I would come here and ask for ya'lls expertise.
House was built in 2001, these are ancient and they are starting to go out one after the other. I was able to take the window out, I took a bunch of pictures. There are a few things I would greatly appreciate some guidance on.
1. Measurement, a bit confused as to what I need to measure here as part of the assembly is broken, theres a part thats stuck/clipped at the top of the gully. I made an attempt at measuring based on what I was able to re-assemble and share it here. Let me know if I am measuring this correctly.
2. The replacement seems to rely on a screw at the top, where I currently have this rectangular hole. Is the idea that I screw above or below the hole or do I need to find a way to screw directly where the hole is?
3. I don't have a scale unfortunately so I will have to wait until I am able to weigh the sliding window part but wondering if I can go ahead and order replacement parts or wait until I have everything measured out.
I believe this is the direct replacement:
hxxps://www[.]swisco[.]com/cl/Series-795-Channel-Balances
But I just want to make sure I know what I am getting into before I buy parts. Once again, I greatly appreciate any help I can get here so we can get these windows fixed.
Thanks in advance
Andy