Not quite the same as mine is a soft top hence the raised bar for the shoulder mount but this shows how I positioned them on the bulkhead. I had static belts fitted to my series 3 so used the same mounting point on the bulkhead they used with some 6mm angle to give a flat surface. Please ignored the dog it is best pic I had to hand, You can see the passenger belt between the strap and the side. I can try and get a better pic next time I am with the vehicle. As you have a hardtop you should be able to use part number 395586 and 395587 for the upper brackets.
I one of mine came from a Skoda Felicia I stripped to take banger racing and the other is a universal seatbelt bought online. As mentioned above you need to be carful with the mounting angle. If taking one from a vehicle it needs to be mounted with the same angle or if buying universal you need to make sure it is one you can set the angle on rather than having to be perfectly straight. (you can see mine are mounted at an angle)