Doug brings up a good point on the springs and weight transfer.
So as long as your going to modify everything to such a great degree, why not eliminate the springs and replace them with counterweights that go up and down opposite of the door? You would have to measure the weight of the door, and build probably 2 counterweights that work off of a pulley system on each side of the door. (possibly concrete filled pvc pipe?)
The opener is still a challange.
Sounds like a fun project.
Why can't the door go across the ceiling like normal?