Hi Plast,
Havok SDK to be used with A6 You will need to know C++ and own a Havok licence to use it.
Newton NGD to be used whith A6 you will need know at less c-script and know the DLL, or Know C++ to use the SDK and make your won dll.
For use a A6 physics engine to make a car you will need a professional version.
The both, Havovk and Newton are exelent physics engines.
The A6 physics engine I never use it, but looking in the forum it's apears to be a great engine too. In this case you need to know c-script.
If you do not want code for your self , maybe you can contract a freelancer to make this for you

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best regards,
Marcio