Heh. I think if you would have mentioned it was 500lbs Rip would have checked out the vid. (maybe he did anyway, don't know). Still a x5 workset would be better if you want general feedback. A PR is always going to be somewhat ugly.
Also this angle doesn't show much about the bar position. What little i can see when you're in the bottom i'd say that maybe the bar might be a bit low, but really can't say.
Personally (i've only been doing LB for 1.5 years and i've only squatted 320 so i'm not particularly strong or experienced) i've had trouble keeping the bar in position and it takes a good amount of force for me to keep the thing on my back. It hasn't caused me shoulder issues, but my elbows have not been happy in various ways. Esp. w/ the weights you're using i think you should be pretty careful to work with lower weights so that the supporting musculature has some time to adapt to this different usage.
There's also a video in Resources -> Videos about bar position that you might want to look at. Also, if you search the board you'll see a fair amount of discussion on bar position, shoulders and elbows.