Just a Comment----from someone who only knows a little about lightweight, FED that races in nostalgia races only.

Unsprung FEDs are lightweight cars. And, they flex a lot under accel/decel. But they can (and do) flex even more while riding in a trailer. So, If you buy a "Flexi-Flyer" chassis a center chassis support is useful while transporting. Something simple will do---we use a carpet wrapped 2X4 under the midplate. We pick up the front slightly to slip the board under.

That brings up the second point-----the used chassis. Is it a bent---also know as a "killed" chassis? Better look real close at a used chassis-----could be the reason the chassis is "for sale"----and the owner doesn't even know why the chassis got eratic!