Hi, I know this a bit late for the original post but...
I've had the same issue. I've done all (most) of the work on the suspension and steering and can add the following suggestions:
1. Check your wheel balances.
2. The rear prop shaft has a metal bush that fits into the end where the rubber bush is. It's inside the end of the steel tube. This wear and will need replacing. It might not have a major influence but it may contribute to over all wobble.
3. My front prop shaft (drive shaft) was BENT - I too was surprised. No marks on the shaft. Did however hit a sand drift on a beach pretty hard dropping down into it. My mistake. This contributed quite a bit to the wobble. No front prop shaft fitted and no wobble until hitting a bump on the highway at 100km/h. Make sure you mark the shafts to the diff and transfer case with a white marker or similar so you can put them back the same way. Easy to forget but make sure you do it.
4. Tighten all steering suspension components and as mentioned before and change worn components where required.
5. Check your tie rod ends (ball joints) carefully. I had suspension 'specialist' missed identifying a faulty ball joint. I live in the country and travel long way at high speed to get to town. My wife and I identyfied this by my wife moving the steering wheel side to side and me looking at each ball joint to make sure it was ok. The mechanic concerned DID NOT do this. I shall not be seeing him again!
After much frustration and a couple of scares at high speed, tomorrow I will adjust the preload the only thing left after eleminating all the others. I'll then moving onto getting rid of the ticking under the bonnet. Already did the valves moving onto the next possible cause :-)
Thanks to Rover Chris
How To Adjust Your Swivel Pin Preload
and all the other guys who help make this journey that little bit easier.
Cheers and all the best.
ps for those using metric 15 pounds is equivalent to 7 kilograms.