I just replaced the stock bolt with something like this. They replace the stock bolt, so I have one of those into the left, then drilled the transmission tunnel and added one on the right, 2 more under the seat for the 6 point harness, and 2 more on the harness bar:
The big washers are used for transmission tunnel, floor 6 point....
and here is my custom harness by The R's Tuning (thanks!!)