The easiest/cheapest and fastest solution would be to use the already defined vehicle physics simulation in cryengine's bespoke physics engine CryPhysics.
You also have the option to use Physx Engine in the latest versions of CE.
To port or reuse existing physics code you will need knowledge on general computer physical simulation, ie, what each part of the code is generally doing as you would have to merge the code. It may be easier if you find that the physics implementation of the vehicle you want to port is already based on PhysX. If not, it most likely would not be trivial, different physics engines have different setups in regards to default values etc so you would have to make you best approximation.
Physics is not easy to make realistic in real-time, corners WILL be cut (optimized algorithms), just depends how far you need it to go. And which physics engine you are most familiar with.