I've not got specific figures for the 400 but the 750s are in the order of 40lb front and 60lb rear for spindle nut torque.
Similar assembly on these smaller bikes so it's not going to be much lower.
The principle being that the components including bearing inner tracks, spacers, washers and centre of speedo drive makes up a complete sleeve along the axle, which is tightly pinched within that assembly prior to mounting it in the forks.