Unlike the other hardening processes, nitriding is a relatively low temp procedure so the core material needs to be treated ( hardened & tempered) before machining. This also removes any decarb from the surface which is a must. Even after a long soak (80 hrs) the depth of hardening will only be around 0.025". The surface will be well over Rc65 though.
The depth is usually defined as to the hardness which equals 110% of the core. Liase with your heat treater for best times and expected depths for materials.
Because of the shallow case this is not suitable for large or heavily loaded teeth.
On the drawing you need only stipulate the material treatment and the case depth. Annealing or stress relieving
 after roughing out will help keep distortion to a minimum.
You will not be able to machine afterwards (except grind) but you can mask off areas to be left soft.

As a rule of thumb AGMA 8 and DIN 8 are about the same then one goes up and the other down from there. ie AMGA 9 = DIN 7 etc. But it is only a rough guide as there are so many catergories to take into account.

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