I must be getting my wires crossed here???? To me it sounds like

Someone has had a frst that has been rotten or crashed and reshelled into a 1.6 shell,

OR

Over the years they have owned it, they've added bits from an rs turbo = a full replica inc engine, body etc....... = not a genuine fiesta rs turbo = no more than £1200

You need to inform your insurance that its a 1.6s with full rs turbo conversion = them asking for an engineers report and then they will insure it as a modified car = if you don't do this you are breaking the law and if you have an accident or get pulled by the police your insurance will be VOID and thats a 6 month driving ban.

I'm unsure if you have already sorted this?????

Sorry mate