Aero aids weren't forbidden back then, it was controversial because the wings and splitters could be adjusted. They got round that issue by supplying extra pieces for the rear wing with the 155 Silverstone roadcar. Then by 1995, fixed rear wings were mandatory, so Alfa struggled with the 155 from then on, as it's main advantage had been taken away.

There's no real issue with VXR's bumpers. They have to make a certain number of roadcars with these parts available, but it doesn't mean they actually have to be sold to the public.