What Michael Orritt said. You need a VIN to be able to find a car at the healeydata site, or anyplace else. The British license plate would be official only in the UK, and I don't believe you could get the VIN out of the UK DVLA with a plate number anyway (but I could be wrong). The good old days when you could get the state DMV to do a VIN search and find out where the car is are long gone. Even if they had a record of the VIN, they wouldn't give you any information due to "privacy", and most DMVs have purged their inactive registrations older than about 10 years.
I would just like to say that healeydata is fine, but the site will accept whatever data is input to it, incorrect, incomplete, or not. There is no one there who "vets" the data or follows up with the submitter to correct it as necessary. There is also no one there who actually uses the data for any purpose. For BJ8s, there is a better place to go: the BJ8 Registry. It has more data than healeydata (more than 52% of total BJ8 production - 9,215 cars), and someone (me) who makes the effort to be sure that data submitted is as correct as possible. The BJ8 Registry is also actively managed and used to benefit all BJ8 owners who have occasion to refer to it with questions or problems with their own BJ8s.