ok i tested it on a grass verge and upon mid rpm launch the revs stay reasonable, car body feels mushy cos its on grass, steering wheel wants to pull left and the car heads towards left.
seems like its working. its not like a 100% off-road locking diff, but instead the clutch would slip portions of the power onto the gripper RH wheel on tarmac which pushes the front end towards the verge felt through the steering.
on an open diff the car would use to just spin the less grippy wheel and steering feels light.
back at home with the warmed gearbox oil i lifted either wheel and i can feel the ramps gripping as normal, more in one-way than the other.
so the diff is fine. phew
gotta clean the filthy car now 
