When I use grease for my diffs/transmissions I generally use Mobil 1 synthetic grease but really Like More_Power said anything that you would use for wheel bearing grease will work like what he uses is perfectly fine too.
Again the weight of the shock oil if you're just bashing the kit doesn't really matter, You can use straight up grease in it and it will be fine. If your racing or running on a track then diff oil becomes part of the tuning process. You can read THIS to understand better how diff oil affects the...
For dirt track in my buggy IIRC, I ran 3k front, 7k center, and 5k rear. I would think youd want to go a little higher than that for running on grass but its honestly prolly not overly important for bashing.
I use Associated diff fluids usually but really most brands are all about the same stuff imo.
If your asking what weight diff fluid that I couldnt tell you as I dont own that kit.