Early in the production of Star Wars, Joe Johnston and Ralph McQuarrie designed Han's "Pirateship" as a long bodied rocket-like vessel. Big engines on the back, a cylindrical body (underneath a lot of structural details) and a nose cockpit. This early conceptual design of the now iconic ship is sometimes referred to as the "Linear Falcon". However, concerns were raised that linear arrangement seemed too much like the Eagle transport vessel of the then airing TV show, Space 1999 (1975-1977).
A model of the ship had already been built, so rather than scrapping the 5' behemoth, they modified the cockpit into the hammer-head configuration we're now familiar with as the Leia's Blockade Runner. The old cockpit was removed, and became the cockpit of the Millennium Falcon we know and love.
Below is a work in progress model of that original design, based on Johnston's studio model, and McQuarries beautiful production paintings.
The scale is based on the 8' diameter of the movie set Falcon's cockpit (a model of which has been transplanted here from my model of the Falcon onto a model of the Blockade Runner body) Greebles were pulled straight off the Falcon as well, making a sort of mock up of what a full scale set of the ship might have looked like. I also used some virtual kitbashing to complete a few details, cutting up models of tanks and trucks to add to the exterior (which is how many of the studio-scale Falcon details were created) The ramp design is based on Joe Johnston sketches.