How I would do it, if I had access to a vertical mill, and only suggesting because of the critical situation here:
1. Using an end mill, flatten an area to be drilled. This keeps the drill from walking, and I wouldn't want to center punch that.
2. Drill and tap to M8-1.25
3. Using flat ended bolt, thread it in and see if it can be forced out.
YOU'D BETTER BE REAL CAREFUL WITH #3 BECAUSE I'D HATE TO SEE YOU RUN A SCREW RIGHT THROUGH THE BLOCK!
If that doesn't work, Center up as perfectly as possible and using as large an end mill as possible but to still leave .005-.010" of cam journal behind and mill out as deeply as you safely can, the goal is to go through the journal without touching the block.
Then, using a pick or small tool pull out the remaining bit of journal if you can.
More than likely, as has been already said, that journal is toast.