E/Stock or F/Stock
You could put factory type upholstery on aluminum skins as opposed to cardboard skins but that would serve as no advantage. NHRA's intention is for the car to look "stock" on the inside and outside and not a race car. Bare aluminum door panels would not be allowed and also would serve no purpose.
I am considering turning my Valiant to a Stock Eliminator car and would have to put quite a bit of "stuff" back but that is no biggy.
Chuck