I'm 95% sure that you need 6 mm bolts.
A curious thing about the Kawi sleds...the engines and I believe the clutches were made in Japan, and use metric fasteners. The rest of the sled was made in Lincoln, Nebraska, using good ol' 'Murican SAE fasteners.
Maybe gixxer6 will post on here with info on the very high grade bolts......I have found that the hex (Allen wrench style) bolts are usually a very high grade compared to regular bolts.....although I don't know what grade they typically are.
Go to a decent Auto Parts store or good hardware and pick up some 6 mm Allen style bolts and give it a try.
Patience is a virtue when removing a flywheel. I like to put Never-Seize on the bolt threads and the tip of the puller bolt.
Torque it down pretty hard, making sure the puller remains "square" with the world. I don't like to go crazy, but tapping the puller with a hammer helps. Tighten, tap, see if you can tighten a tiny bit more, let sit overnight and try for a little more torque the next day. You will get it.