It has both a hole behind the front driver and passenger seat in the floorpan (with longitudinal tabs under the car) that were originally designed for a lap belt anchor, which then used an L bracket for the 90 degree turn by the rocker on each side, respectively, and then the other side was just simply attached by a mounting point within the transmission tunnel.
Here's the rear mounting point:

and a view from under the car:

Note that this is *stock* and already on the car from the factory.
I used those to install a four point harness for the driver (mounted at three points through use of a Y belt) and a 3 point retractable belt for the passenger, appreciating that ideally the mounting point should be higher than the shoulder. That's not going to happen without a roll bar. I understand that in a front impact a lot of force is going to be transferred through the seat back by the belts and that it's just going to bend... that's better than no force at all which is the scenario with just lap belts...


(I still have to install a shoulder guide on the passenger side.)
In pulling out the back seat, the mech discovered four holes. I hadn't spotted them at first, likely because they were full of dirt, but they were there. He tapped them to clean up the threads and we're good to go.



Purchased the three point belt for the passenger front and rear lap belts at Seat Belt Planet.
Edit:Added pics.