No idea what the side cutting boards are for. Maybe used to brace a more aerodynamic wide body is my guess. But, I'd totally do that center chassis brace/skid plate thing minus the button head phillips screws of course. I always added weight to my 2wd off-road SCTs/STs to better handle bumps/ruts. This Rustler oozes on-road use only.
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Just ask the seller what in tarnation is going on with their ride.
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I almost bought a center brace/skid for my SC10 years ago to add weight down low...
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I'd buy that eBay Rustler if it were in the neighborhood of $110 just to beat the snot out of it... get it out of my system. Rustler parts are cheap. Replace with stock parts as needed