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I don't know for sure in the case of this car, but usually graphite is lighter and more rigid. Unfortunately, it's also more expensive. The graphite chassis and top plate that come with the David Jun edition car make it very rigid, so that would be a good choice. I would guess the kit will set you back around $100, though. If you don't have a local source for it, try
www.mdiracing.com. Send Les an email. He's a Tamiya guy, so he will look long and hard for your esoteric Tamiya special order requests. He goy me a brand new F103L T/93 Lola body. Now that's not an easy body to find!