If you have not done so already, you should look at the rear wheel drawing in
the parts book for your bike.
do the inner nuts serve to stop the wheel moving side to side
Partially ...
The inner nuts (one on each side of the wheel) on the "Wheel spindle" sandwich everything from the brake plate on the drive side (left side looking forwards) to the speedo drive on the timing side (right side looking forwards).
What locates the wheel hub on the Wheel spindle is:-
. the drive side wheel bearing is locked in position in the hub, the timing side bearing is spaced from the drive side bearing inner by the "Distance tube" between the bearings' inner races;
. the drive side bearing is prevented from moving away from the Distance tube by the "Retaining ring";
. the timing side bearing is prevented from moving away from the Distance tube by the "Distance piece" between the bearing's inner race and the speedo drive and the "Speedometer adaptor" between the bearing's outer race and the speedo drive;
. when the inner nuts are tightened, the combination of Distance piece and Speedometer adaptor should prevent the non-rotating part of the speedo drive being squashed against the rotating wheel hub;
. note the washer between the speedo drive and the inner nut on that side;
. note the inner nuts are different part numbers from each other and the outer nuts; the inner nuts' different part numbers signify different widths; the different inner nuts must be fitted on the correct sides of the hub to ensure the rear wheel's centreline is directly behind the front wheel's centreline
do I just tighten the nuts together onto the swinging arm.
No. All wheel hub parts assembled correctly, the inner nuts should fit (almost?) exactly between the inner surfaces of the ends of the swinging arm. When each outer nut is tightened it should clamp the corresponding swinging arm end and chain adjuster between the outer and inner nuts on that end of the Wheel spindle. Having used the inner nuts to clamp all the hub parts together, you should not need to loosen either inner nut to clamp a swinging arm end between an inner nut and an outer nut.
as things stand, the speedo drive seems free to float out of position. The section (F) in the manual does not give any guidance as to what holds the speedo drive in position.
As I have explained above, the inner nut on the timing side end of the Wheel spindle clamps the speedo drive in position against the Speedometer adaptor; the Distance piece between speedo drive and timing side bearing inner race should prevent the inner nut squeezing the speedo drive against the hub.
You have seen the inner moving ring of the speedo drive has two square blocks 180 degrees apart and the Speedometer adaptor has two corresponding square notches?
