Hi Sean,

It doesn't really matter where the car came from originally so long as it has been imported correctly into the North and used there by a private owner. Make sure you gather as much paperwork as possible to prove that before you bring the car south of the border. 

You then have seven days to book an inspection with NCTS, which is responsible for determining the taxes owed. From what you've told us, there should be no VAT or import duty owed, and VRT on a classic that is over 30 years old is a flat rate of €200.