Here's another picture showing the relative heights. Each spur is resting on a standoff of the exact same height. The standoffs are sitting on the gear mounting plane. You can see that I can't shave enough off the Kyosho spur for the outdrive to reach inside the diff enough, while still being able to use a bearing. Don't forget, I'm limited by the length of the outdrive, not so much the diff mount...
And even if I could get this to work, I'm still stuck trying to find a bearing...