Have you checked E-Bay recently for parts?
I just picked up a Battery Mount Post Set, Battery Pressure Plates, and some Wheel Hubs that were the missing pieces to a nearly complete MX-4 I picked up around Christmas.
I'd really like to find a NIP graphite chassis plate. I know I can get one through FiberLyte and more than likely will.
The one that came with my car had some dremel work done to it to add battery straps which eliminated the battery post mounting holes.
Just looking to restore mine to go on the shelf so its got to be right.
Gosh these things get expensive.
