You'll almost certainly need to ream out the 8mm, because you'll be lucky to find a boring bar that small - plus boring bars can "chatter" and cause poor sizing / finish. As a guide for reaming, the hole needs to be drilled 7.5 - 7.8 mm and finished with the reamer. Beware of putting an undersize diameter hole on an 8mm shaft, otherwise you may find they split and become damaged (esp with the 2 holes in the side, which will weaken it).

What are the two holes "pins or grub screws" for?