
The Expert will be specific knowledgeable people at the Department of Transport, Arrive Alive Communications, the Road Traffic Management Corporation or others who might have the expertise to answer the question.
I'd suggest going to one of the baby stores...they normally have quite a wide range of seats...perhaps they have one that can be secured by the lap belt only. In terms of installing a belt, I'm sure a Ford dealership could advise you on the complexity of the task. If it were me, I'd go to a scrapyard and remove a rear belt from a crashed later model Laser / Meteor / Mazda 323 (same model) and just bolt it in. (Obviously, make sure that the belt wasn't occupied at the time of the crash or it may have been stretched and weakened.)