In their original form, Chevy sixes were fairly efficient if you kept them tuned well, and they were relatively stout and dependable; they are, today, basic mechanics in practice, and old tech; they are a good foundation for a decent engine. There are several sites on the internet that are focused on straight sixes (and eights): search "inline six cylinder engine" or "Stovebolt engine", or "Inliners International" and wander about. As to doing something with your engine, I like what falconvan said about that injection setup he saw.