The wrench that comes with the bike in the standard cheesy 80's Japanese toolkit would of course be ideal. However, I assume that you don't have that.
This is a picture of a tool that one of the members of the Yahoo group fabricated from some flat sheet stock. I think that you need to sign up with the group to see it, but that's a good idea anyway.
The 350 has a system where the adjuster is built into the swingarm and can be done by hand. That makes life significantly easier.