Please do a lot of research before even considering importing a car into Greece ,classic or otherwise.
unless you have all the documents including the Certificate of Conformity you will just have problems.
At the top of this page Hot topics and links there is a section Importing a car
with a reference to classic cars.
There is also a classic car club on Crete, think it is based in Chania but not sure, try searching the web ,they will be your best help.