Stop me if this is trodden ground. What about featuring an engine. The Wright Cyclone family (and it's various copies and license-built versions) powered everything from the Polikarpov I-16 to the Constellation.

The Wasp family covers the MC 200 to the Sikorsky H-5 to the Spruce goose.

Other engines like the Merlin and the Spey have pretty good families but nothing so big as those two I think....