I've used Wesco seat belts in a couple of 240Z's but damned if I can remember which version it was, the kind I bought had the reel mounted right at the end of the quarter window, Is this it?

https://www.wescoperformance.com/haandco3rese.html

I used the roadster belts in both of my Z cars. Yes, the retractor mounts near the quarter window.

Here's what you're looking for: https://www.wescoperformance.com/noname.html

+1 on the Roadster Retractable belt with the 11" sleeve.