Did you drill or cut off the end of the plastic throttle boss as it's not open ended?I sure did!
Yes, there is a 2 cm long plug at the ends of the handlebar. They are a hard aluminium plug that's perhaps only glued in there? Can't really tell in the pictures, but on the throttle side where I got the grip off, I could see past the plug on one of the sides, and couldn't find any evidence that they are welded in place. But I could be wrong thou.
I just made good of the plugs, and drilled a whole into it, and insertet new threads into them, in case the aluminium would weaken with time and start to slip. Don't wanna do the job two times.
Was rather easy when I got the tools and parts needed to get the job done.