RE: Judo specific grip training
Try getting athick piece of material (similar to the material worn during competitions) then is long enough to throw over a standard chining bar leaving enough free for each hand to hold.
Grip the material as if in a competition and perform chins to mimic the pulling during fighting whilst incorporating the grip work. This will be as similar to judo as you can get without doing the judo.
Decide on the optimal number of reps then add weights accordingly