Was going to put the transaxle back together this weekend, but I just talked to my brother and he knows a couple of other local machine shop owners. He's going to ask them about this project next week.
EDIT: already heard back from one of the shop owners who wants to test cut one of the gears to check for hardness - same concern as the first machinist.
I'm assuming the best case would be if this stuff is
case hardened. Once you cut through the outer wear-resistant "skin" you reach metal that's more easily worked, so it's more practical to machine the old fashioned way (non EDM).