A stiffening assembly for a vehicle cowl panel includes a pair of cooperating C-shaped brackets. Each of the pair of cooperating C-shaped brackets comprises cooperating bracket arms adapted for holding opposed ends of the pair of cooperating C-shaped brackets at varying distances from one another. Each of the pair of cooperating C-shaped brackets comprises a pair of parallel bracket arms which align with one another when the stiffening assembly is attached to the cowl panel. Cowl panel and instrument panel assemblies incorporating one or more stiffening assemblies and vehicles incorporating the cowl panel and instrument panel assemblies are provided.