Rear seat belt help

[Triothreetrio]

I've read all the threads on this ,I have a holdsworth and would like to fit a 3 point on the non wardrobe side
Ive no upper mount I have the 2 lower as lap belts fitted
First ? Bolt though at air vent does ,the plate with captive nut need to be welded in place or just bolted
Next ? Where do you get the seat belt that has two clips so it well out the way when camping
Cheers