If its registered in the owners name the easiest thing is to get him to apply for a lost/replacement tax book. Its probably not though and prob came from ni. The plate isnt real anyway but didnt expect it to be, given the number. Might have a few hoops to jump through to register it.
There appears to be an effort made to make it a bit more presentable in the pics. Tinwork has been painted recently and rest of it painted in the not too distant past. Lots of rust coming through. Lots of work to be done to make it tidy and still have the usual expected mechanical work. He has had plenty of views but no quick sale.