H165 diff is the biggest you'll find that bolts straight in and can take a fair bit of punishment. They range from 3.9/4.11 to 4.875. (easy to find) And I think vannetts went higher.I'm sure Nismo had H150 for the race cars and lsd are rare. You can just weld the gears and make a lsd is one option. Do a diff swap which can be expensive or spend big bucks and maybe find a lsd. Im sure there are plenty H165's in your bakkies and cheap.