Prototype one, the red car, featured a stainless steel monocoque, while the second, yellow car used a chemically bonded aluminum honeycomb structure developed with help from Alcoa, similar to what would later be a production first with the MKI Elise. Both cars shared a similar two piece (upper, lower) composite body styled by Carrozzeria Scaglietti. The twins were powered by a mid-mounted, 300 HP, 4.0 liter version of the 328's 3.2 quattrovalvole V8, though longitudinally placed in contrast to the donor car's transverse layout. Drive was distributed four ways by an intriguing hydraulic system of which I unfortunately can't find any detail on. In order to accommodate said drive mechanism, the engine was heavily offset to the right hand side of the 408's chassis.
Trotted out to all the big name magazines for testing and promotion, the 408 created a lot of excitement and speculation before Ferrari pulled the plug on its consultation ambitions. The yellow car still exists and can be viewed at the Galleria Ferrari in Maranello, while from what I gather the red car's whereabouts are unknown.