Hey Guys,
Firstly chestnut is the same as a tan interior for 1970, except in 71 the interior was not a full Tan/Brown onterior, they used Black interior parts also, black parts were seat backs and consoles where applicable. Red interior is still just as hard to find as Tan/Chestnut.
The interior color is pretty rare, but the thing that makes this interior even rarer is the fact that it is a Premium Gran Coupe interior for 1971, super rare, premium interiors for 1971 Gran Coupes are the rarest interior in any E-body, regardless of the color, color just makes it even more rare.
The original color combo on this car would be fairly strking, the color when new is like a rootbeer color more than a brown, and the chestnut interior would complement it immensely.