Yes, it's quite possible to do 68k development on a PPC. I believe you can even develop System 6 apps, although I haven't tested it yet.

I'd like to expand the tutorial to the point where it introduces the user to all the basic Toolkit functions and guides them through the process of creating a standard Mac application with DAs, menus, saving and loading, etc. It will probably be a work in progress for a long while though, there's a lot of ground to cover.