that gadget is a compensator valve

so basically the more weight the car has at the back he valve has something inside it possibly a ball bearing, so it increases the braking pressure accordingly to the back, 4wd are built onto the valve block on the inner wing

the ecus and abs looms are different aswell as sensors

the pumps are different aswell as they swapped the bottle over

when most people convert to 2wd from 4wd its easier just to take the shafts apart and leave the cv joints in so they use the 4wd sensors still