Pillock said:
i'd only fit them to a car which had mounting points... there's a hell of a force pulling on mounting points during an accident and you'd need a lot of work to make your own mounting point.even 70's bugs, and from memory late 60's bugs had proper factory mounting points that modern seatbelts screw straight into, standard fittings. maybe this is a feature of german cars... worth pulling a few backrests forwards and seeing if there's nuts welded to the metalwork!
Likely to be a result of US legislation.
I would still check how solid the bodywork around the mountings is on any car. Ideally they need to be on a good hollow section like a sill or a B post, or at a join between two or more panels. A lot of C posts are single skin and would be easilly deformed by a point load.
It shouldn't be too difficult to fix up your own mountings as long as you think carefully about the way you do the job, and make sure your welding is up to scratch.