Toyota 4Runner in UAE

Hello everyone! My brother's about to order a car. He's interested in the LTD with full-time 4WD for driving on highways in wet weather but also likes the Offroad version with rear locker + KDSS. So, I have a few questions: 1) Can the LTD have a rear axle locker installed? How about the ARB air locker, is it a non-destructive modification, and how's the quality? 2) In rainy or snowy weather with the Offroad version, what happens if you drive fast in two-wheel drive? Isn't it unsafe due to slipping? If you switch to H4, does it have a center differential, and what's the maximum speed you can go (80 km/h)? 3) If we end up buying the LTD, can we modify it with the TRD front bumper? The TRD front really looks good. Thanks, everyone!

What type of fuel should a 4Runner use?

I'm wondering if anyone knows what might be causing a noise from the rear wheels of a 2006 4Runner when going over bumps?