Tony
You need to make a bar that runs across behind both seats. It bolts into the shoulder seat belt mounting point on each side. You need make it so that it runs in line with the angle section in the engine bay under the inner rear window and to also bolt to that angle section. But do not overtighten these bolts as the window may crack! Then you attach the eyelets for the harness straps to that cross bar. That was the factory way of doing it and it is how I did mine and has worked well for the last 17 years. And if you are making your own, put in some holes with 6 or 8mm threads so that later on you can bolt on a video camera mount!
I don't have any pictures on this one, but I am due to whizz my seats out soon so if you want a picture or two let me know. I made my own bar so this is not difficult to DIY.