Finally I bite the bullet and made the purchase last week…
Just that I am stumbling into a weird crashing error which can only be solved if I commented out body->AddCustomPhysics(onCalcCustomPhysics) in UFGearSkeletalMeshComponent class.
My class structure is a bit complex though… simplified explanation is I created a C++ class name BaseVehicle which derive from FGearVehicle. And this BaseVehicle is later made a parent to BP class where only in this bp class that mMesh (vehicle skeletal mesh) is filled (otherwise null). Probably this contributes the crashing error but I am still looking for an answer.