Here is a long crack in the side of a guitar. I first apply the glue in the crack, I use these donut magnets (one on the inside and one on the outside) to bring the sides flush, then I use spool clamps to close the gap. After the glue solidifies I will reinforce the back side of the crack with kerfed strips of mahogany. It should be stable for another 50 years. I handmade these spool clamps 35 years ago and they have earned their keep 100-fold.
Sorry the pix are out of focus, my 61 year old hands are a bit shakey.
How can you tell that the stage is level? When the banjo player is drooling out of both sides of his mouth. Till next time, Al