My brother recently finished up his 70 Challenger with a green interior, for starters he had the 'bayou green' paint mixed with the codes taken from the 1970 parts catalog, and redid all of his interior metal pieces, dash frame, steering column, etc. as called out on the same page of the catalog. He also had SEM vinyl dye mixed to match the paint and sprayed that on his dash pad, console, door & kick panels, seat backs, rear package tray, etc. IMO the result looks really nice and coherent, would it be totally correct, no, but the carpet, seat covers, headliner still do provide some of the color variations.

I guess in hindsight, mixing up a few similar but different shades of dye for the various soft parts would yield the most authentic result, short of using all NOS parts- which would seem to be almost impossible these days.