My bet is you could tell them the critical dimensions or even ship them a differential and say what ratio gear set you want in that case, and they would do the engineering.
Kurt
Exactly, no need for us to guess how the pro's might go about figuring tooth geometry and such or telling them how to make the gear.
Anyone with the machines to make them and willing to do the job should have the know how and understanding to tell you how they'll do it and what info they need.
I suspect the offset between carrier and pinion centerline (they don't intersect) as well as offset between mounting surface on the carrier and pinion centerline are the critical dimensions.
...Gear
manufacturing is really a specialized business that takes a lot of know how.
