I will start with a 370Z as a quick import as its easy seeing parts aren't all over the place, then ill replace the Skyline seeing the definitions are on the skyline which might be easier. :)
You can do this with any custom car model its not gonna change really.
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For part definitions go here: http://forum.turboduck.net/showpost.php?p=146377&postcount=2
Tools you need:
[Trial or Full version of Zmodeler 2.2.1] (If trial you will have to download the Al