The main reason the Columbia was used under the Fords was the shape of the frame. The X crossmember shape and the fact that the legs at the back of the transmission were the rear motor mounts made it virtually impossible to fit an overdrive to the back of the transmission. They moved the planetary gearset to the driver's side axle housing. The left housing bolted to the banjo-shaped center carried the planetary and the vacuum shifter.

One other bit of trivia about the Ford rear end- - - -it was not a hypoid design- - - -the pinion gear meshed with the ring gear on center, which made it necessary to have a floorboard tunnel a couple of inches taller to clear the torque tube on the passenger cars. It was also possible to "flip" the carrier housing on reassembly and end up with the ring gear on the wrong side- - - -one forward speed and 3 reverse gears!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!