You might want to check on those diff gears. I know HotBodies also has HBC8101-1 that are labeled as hardened steel, while the HBC8101 are just labeled as steel. They could be the same, but I would get the -1 version just to be safe.
http://www.hbeurope.com/piw.php?part...8101-1&lang=en
I am using these gears in my Jammin on-road diffs, but haven't had a chance to test them yet. They seem like they should be very solid though.
If you are thinking of using Kyosho 777 diff case, you can also use Jammin cases, which are the same as Hot Bodies too. Nova RC makes alloy cups, which I also have but haven't tested yet. Innovative RC in the UK also makes alloy Hot Bodies cups.