Those pictures are for all 722.6** boxes.

Yes, anything flexible will do. You only have to mark the end using the measurements above. After all its only a bit of plastic attached to a coily springy thing. Take a look at your engine oil dipstick, theres nothing special about it, its just a bit of metal with a couple of lines on the end, and a handle/seal on the other. Since the gearbox dipstick isn't supposed to stay in, you don't need a handle or a seal.

It just has to hit the bottom of the sump, thats it. Why pay good money for something you can make yourself for nothing?

Use a bit of mains electricity earth cable if you like!

Oh bear in mind I'm not sure if US inches are different from UK inches, over here an inch is 2.54cm.