I have run the car briefly, but not properly. But with regards the diff balls, I remembered that we quite often run diffs with half the balls removed (every other one) to reduce the rotating mass. And it was fine back in the day. Of course, that means it would be fine now, unless you want to run a hotter variety of brushless motor. And in that case - you would need to see how far you can go..
These projects are still maturing with age.... I've collected a few new bits, got the shells I want, and then - that's about it! Work work work... There's no rush
