In the US they just need to be registered and inspected in your home state. Registration is different in each state though. I have a CMC Porsche 356 Speedster which is based on a slightly shortened (10.5") '69 VW T1 (Beetle) chassis. It is registered as a '69 VW so all the safety and emissions laws for that year apply. Cars built on custom (tube) chassis are more difficult to register. I'd think a VW based car would be ok in Greece. Germany and Sweden seem to be the strictest and they are ok there. There are also kit cars based on the Datsun/Nissan 240-300ZX and the Pontiac Fierro --- even the Skoda has a kit available for it.