After you build the chassis, but before attaching it to the avatar, attach your car frame to the back cross-member of the four-bar linkage. That is the "stationary part. Attach your car wheels to the physics wheels.
You can select all the chassis parts and scale them all at once. Scale so your front wheels match, and then move the rear into wheels and shocks into place.
Download the Persona I made here:
Import Persona from the right-click menu, drag & drop it, or put in your Persona folder to load by double-clicking it.
Widget not in any sidebars