Several hundred internet searches later / Multiple Forum Searches...
Plenty of choices for Pre-96... the vendors even have different part numbers for 2 Door vs 4 Door.

ZERO Answers for '97-'01 XJ's
Even if I wanted to pay $300+ for each factory set-up, they are discontinued.

What have people used to replace the Factory 3-Point, Self Retracting Seat Belts?

 

The only difference between the 2 and 4 door versions is the bottom anchor. If you don't use the bottom slider, you can just bolt the seat belt to the floor with the stock bolt. It all depends on how much you need that belt to slide back for rear seat access. No big deal to me since the kids are all grown

 

My 98 OEM setup is not attached to the seat, so that is no biggie.
So you're saying the pre 96 and post 97 front seat belts are the same length?
and
the 2dr, with a wider door opening, is the same length as a 4 dr?

 

That is correct. Also the pre 96 belts do not attach to the seat, but to a rail that bolts to the floor

 

Cool... Stopped by Summit Racing yesterday and grabbed a pair of these Corbeau universal belts:

https://www.summitracing.com/parts/csu-43321b

I'll just have to transfer the mounting bracket for the retractor. This Weekend- Seat Belt Replacement & Broken Drivers Seat Frame Repair, hear 😁 I come!

 

Cool. Pics when you are done

 

I just wanted to throw out there that I have the complete rear seatbelts that I just pulled from my 98. They are in great condition. Let me know if that would help anyone.