Converting GP4 cars to GP3

I don't even know if this is the correct forum to post this, but there is a way to convert GP4 cars to GP3?

I'm asking this because there are some GP4 mods that I would like to see on GP3, granted if there is a way to do it.

Or do I have to manually create them one by one?

Not possible unfortunately. GP3 is too old, which means only one shape for all the cars and a relatively poor 3D model & hard to alter.

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So, yeah, I have to manually create them one by one, in poor words