Nasty Break!
OPs' link shows an excellent repair, probably pricey but well worth it, as you can see by the pics, it's pretty labor intensive to do. I believe most of these had a fiber overlay that the crown and Gibson logo are inlayed into, replacing that wil make the repair pretty much invisible from the front side ( even if yours' dosn't have the fiber overlay ) you may want to discuss using one anyway to add a little strength and the inlay may be a little easier to do "off the bass".
All the old glue gobbed into the break will have to go and it looks like you don't have a lot of surface area to work with, in other words it's a short break not a long one. A good repair artist ( I never like to use the term luthier ) could also replace the headstock entirely, using the same grain "painting" technique to blend the repair into the neck, that might be the way I would go with it as the break is across the tuner holes in a spot that dosn't have much wood anyway.
I know it looks bad, but the rest looks to be very nice and the repair is absolutely "do-able".
Good Luck and keep us aprised of the progress,
Scott ( BassVI )