Something different Building for MPG.

This past August at Moparfest in New Hamburg I met a guy that had put a Dakota V6 and OD trans into a 71 Dart, Painted up all blue and nice, looked just like a 318, actually did a double take (why is that engine so small) Started talking to him about his car, it seemed everything was done on the cheap including a Mako paint job that actually looked good. Anyways, with this Dak 6 and OD he was getting mid 30 mpg, but that is imperial gallon, not US but still impressive. He said he had more than enough performance with this combo for daily driver that desnt kill the wallet. Why cant the current automakers see this...