If you email Richard at Nubodi
and ask for a BMW Z3 buyers guide he will send you one free. He wrote the article for Car Mechanics magazine and Kitcar.
It explains what to look for when buying, all the model choices and options, explains 'facelift' and 'widebody' and other terms, horsepower's, etc
More importantly what are the important things relevant to the donors of these kits.
It was invaluable when I bought mine.