My brother had to do it with his 73 Pantera.
Basicly, it needs and engineers report, to say that it complies with all the ADR's applicable in 1969.
His engineer handled all of the paperwork, the VASS, Engineers Report, and the RWC.
He dropped the car off, got the report, took the car back and fixed it all, then took it back for the final inspection.
In his case (1973 car) it needed headlights (so will yours) Seat Belts (so will yours) and brake hoses (maybe yours will?) and whatever else they pick. The Pantera seats are velcro'ed in, and the wipers are very small, they both had to be modified to comply, longer wipers and arms, and the seats bolted in.
It was done by Archie Robinson in Bayswater