So I'm heading up to Michigan's UP this next weekend with my wife and 3 kids. I realized I had a problem being that none of them are in carseats anymore; the middle seat lap belt.
Those of you with 3 kids can relate. Using the middle seat lap belt quickly turns into "which kid do I care about the least?" or "which kid will best survive with only a lap belt?". LOL
So here's how I fixed it.

I grabbed the drivers side rear shoulder belt from my 95 D1. Cut off the upper retainer piece.
Bolted it to one of the drivers side jump seat belt mount holes. This worked well because there's a centering peg already there to align the retracting part vertically.



Bolted the other end to the stock location in the floor.


Finished product. Works perfectly.

 

Definitely some ingenuity, think this was one reason I wanted to look into d2 seats, hell I used to let kids sit in the rear jump seats belted in boosters lol , my kid was pissed when I removed them

 

Yeah I was exploring different options and they all kind a sucked. I thought about bolting or welding a bracket to the floor but there's a marble sized SS ball inside the belt spool thing that causes the belt to lock up if its off in any direction by more than a few degrees.
Putting that spool on the floor also would have meant it would be prone to getting hit by cargo. Mounting it to the back of the seat also wouldn't work because it would be leaning too much in one direction and there's really nothing substantial to mount it to in there anyway.

I feel pretty good from a safety standpoint about using all stock seat belt hardware and mounting locations.