Here's one thing you can try to help put yourself a bit at ease.
The forward most screw on the right side of the revolver is there to retain the crane. With a proper gunsmith screwdriver (so you don't bugger up the screw head using a cheap Stanley
) remove that screw.
When you do that, you can pull the crane forward and remove your cylinder from the revolver.
Remove the cylinder completely from your 686 and then casually fit the crane back in to the revolver with no cylinder. You should see with a fine eye and also "feel" how precisely that crane fits in to the frame. It fits as nicely as your head on a pillow. Just putting that piece in there and "closing" it will put your mind at ease. It should come to rest and look like Horace Smith himself fitted that crane to the frame.