Well I don't think they can legally sell it as new.
Land rover actually did something similar with the V8 Defender, they wanted to build one for the 50th anniversary of the defender but there was no chance a "new" defender model would have been been able to go through regulatory approval on that old chassis, so instead they bought hundreds(thousands?) of old second hand defenders off the market, restored them to factory condition and retrofitted them with a brand new V8 engine, gearbox and interior. But those were never sold as "new", your V5C document would always show it as originally registered as whatever the car used to be before the refurbishment.
gambiting|4 years ago
Land rover actually did something similar with the V8 Defender, they wanted to build one for the 50th anniversary of the defender but there was no chance a "new" defender model would have been been able to go through regulatory approval on that old chassis, so instead they bought hundreds(thousands?) of old second hand defenders off the market, restored them to factory condition and retrofitted them with a brand new V8 engine, gearbox and interior. But those were never sold as "new", your V5C document would always show it as originally registered as whatever the car used to be before the refurbishment.