This to be done in two stages, initially, using DMR-JAPAN Primary Gear Holder TL006 ( 2 Bolts securing it to the Crankcase ) to lock the Primary Drive Gear & undo its Bolt.
However, leave the Gear in place for the time being as it makes it a little easier to rotate the Crankshaft and get the Pistons in the right place to remove later on, unless of course you have removed the Cylinders beforehand.
The Clutch Primary Drive Gear was removed a little later on (not in these Images) and also the Kick Start Mechanism was removed before it fell out!!