Steve,
I wonder at this hypertrophy. Your spinal extensors would only be hypertrophied due to certain reasons... one, a neurological reason (which is extremely doubtful), and second, overtraining on one other side. Your description definately helps in that it sounds like a imbalance is your pelvis. This can happen because of an anatomical leg length inequality, or trauma, or simply side dominance.
I also wonder if you have developed some about of scoliosis, which rather than spinal extensor hypertrophy, would actually be rib humping to one side. One thing you can do is see if that hypertrophy seems to disappear when you bend forward (ask a friend to observe), as well as the tilt. If it does not disappear, i would definately suggest a structural scoliosis, if it does disappear, then i would suspect a functional cause of the hypertonicity.
That being said, i would guess that most of your problems come from the pelvis, and like you said, as i cannot see you, this is very difficult to simply say exercise thus... but anyhow, sidebending exercises with weights are a great exercise to stabilize the whole spine. If you are sidebending to the right, most likely you will want to weight your right side as you bend left. I would also guess based on your discription, that you have a easier time turning your torso to the left and a harder time turning your upper torso to the right. Therefore, see if you can work out your transverse abdominals towards the harder to turn side, or the right if my guess is correct.
Next, (difficult, may depend on you), look at when you stand naturally, at which leg turns outward more naturally. That side most likely is going to be your right in your case (but not necessarily). That side is going to be the side wher you are going to work out your internal rotators of the tibia (specifically the popliteus). This can be done with stabilization exercises (one legged squats on that side) or simply by with a theraband, turning your foot inward (medial rotation of the tibia). On the opposite side(the right), you'll want to work out your hip flexors, the psoas in particular. This can be done with external rotation of the thigh, and hip flexion at the same time (to isolate the muscle).
Besides that, kinetic chain wise, check to see which piriformis is weaker (just palpate at the glutes for the low lying glut, probably again righth in your case) and you can also exercise that. But again, that is all i can suggest without seeing you. If we ever get a chance to meet up, give me a shot at it, and I probably could clear it out in 2-3 treatments... if not 1... but as you are living way out there...

, those exercises are the best i can suggest. Let me know how it goes, and try it!
hope it helps
ken