How important is numbers matching?

Bought a 1972 340 H code from a restoration shop where the owner said the spare motor & trans was numbers matching in the AD. After purchasing car & getting it home;I find out nothing matches by the numbers! To me it doesn't matter since I'm going Viper red on the car & changing the interior color to black.I guess if I was going concourse restoration I would be screwed . Still sucks that I overlooked that important part of it & trusted what was said.:banghead: