Hey man, long time lurker/follower of your build. I'm currently mimicking your setup with the lap belt as I've found your method is the cleanest way to accommodate an aftermarket seat. (Sparco QRT-Rs in the mail now!)
These photos give a basic idea of how low the rear of the seat is able to sit.
It looks like the PCI rails that I ordered are a slightly revised version of yours, and I'm starting to think that the mounting point hole on mine is slightly smaller.
I wanted to double check the orientation that you have the Schroth SR S65 sleeves. It doesn't seem to slide neatly inside the Schroth lap belt bracket hole, or in the PCI mounting hole. It is supposed to slide inside the PCI bracket hole, correct? Hope I'm making sense.
Here's a quick photo to illustrate my issue:
If the PCI mounting hole is indeed smaller, then it looks like I will need to widen ever so slightly it to accommodate the sleeve.