[HO455]

Welcome aboard.
Most likely the reason you couldn't find any information on removing the headliner is that most of them have removed themselves by now.
I can give you some tips from when I built a replacement for mine.
If your removing the entire headliner start from the back as I believe the factory installed them from front to rear. Where the front panel shoved into the front and side rails. Then it was trimmed if necessary to line up with the first rib and the then the second panel was inserted between the side rails. It may have been trimmed to allow it to match the first panel before the first bow was installed. Once that bow was installed the next panel was fitted. And so on to the back.
This is just my opinion on how it was done from having several partial panel sets that I used for patterns and comparing them to other people's posted panel dimensions. I found a fair amount of size differences suggesting that the panel were trimmed during installation.
As far as I know you do not need to bend the side rails. There should be enough room to push the panel up and then pull the sides in to clear the side rails. Not a one person job. 2 people working together using some shim stock to hold one side so it will be able to slide down over the side rail. (Shims like what you would use to hang a door frame.) Then once one side is past the rail the other side should be able to be pushed up and the panel side towards the first side. This should allow you to get the panels out with little damage.
The plastic bows snap onto the metal ribs. The fit very snugly and after this much time the plastic has hardened and is now brittle. Using a hair dryer to soften the plastic will help, but be careful not to singe or discolor the fiber board panels. I would recommend modifying a flexible putty knife to fit under the center part of the plastic bow so you can pry evenly when trying to get the bow off. Spraying silcone spray or WD40 under the bow as you go may help, but it also may discolor the fiber board panels.

THE BOWS ARE EASY TO BREAK AND ARE HARD TO FIND.

If Richard2717 doesn't chime in on your thread send him a PM. He has parted several Burbans out and seems to have a good technique for removing the bows undamaged.
I'm not sure it will help but here's a link to the part of my repair thread where I am replacing the headliner in mine. Starts on post 283.

http://67-72chevytrucks.com/vboard/s...698377&page=12

Good luck and we would love to see some pictures of your Burban!