Jack the vehicle MUST be registered as [historical]. That includes [historical] insurance. Once that is in place you can use the original plates. BUT- the plates MUST have been in use at the time of the vehicles manufacture. So if he had a 1968 car but it had later issue plates he would need to get the plates in use in 1968. I have been saving those too, for my 1968 Firebird convertible. The Custom Plate Unit handles this but if he calls the DMV Title at 518-486-4714 they can help direct him to the right place.
