The famous American folk hero lumberjack Paul Bunyan's best friend was his blue ox, Babe, but he also had a dog, Sport. There was a problem, though, and that was that because Paul was a giant, maybe 30 feet tall, his normal-size dog couldn't keep up with him in the woods--Sport could run to keep up, for a while, but always got tired and fell behind. Paul had an idea, though: he started putting Sport's dinner dish under the front of his dresser. Sport had to lower his front end to get to his food, but his back end could stay standing outside. Eventually, after a few months of this, Sport's front legs started getting shorter and shorter, accommodating to make it easier to get to his dinner, but his back legs, not going under the dresser, stayed the same length. The result was that being shorter in front, and higher in the back, Sport was always running downhill, and so he never got tired following Paul through the woods.
One day Sport got cut in half by accident, and put back together wrong. . . but that's another story. . . .
If you put your tall camera back behind your short camera front, you're going to have the equivalent of Sport--a camera that's always looking downhill.
That's aside from the problem of getting everything fit on the same rail and moving, if you want the back to focus, too, and then there's the problem of folding it all up. I wouldn't assume at all that either the respective tracks or gearing, or relative placement of the gear to the rack, have anything in common. It's not all insurmountable, but maybe not as easy as you might initially think.