Are your current stock ones broke? I would not replace the whole diff case unless needed. Just open up the current ones, check mesh replace shims, if needed, clean out old fluid and refill. Reinstall and go.
Pls don't laugh at me...
I have not even got it yet.. my first car ever.
Its on its way from US.. should arrive next week..
As far as ive seen on the internet- Arrma cars arrived with no diff oil.. loosen bolts..ect.
So i thought to run a checklist... and to shim the diff on the way..