Dave, I still have not solved my front fork shudder I described in a post awhile back. You suggested wheel balance. I was just interested in this post of Aug 18/05 (below) of tale wagging the dog. I just noticed the wear on my rear avon tire . It is below the wear indicator on one point and on the exact opposite side there is considerable more tread. Why? And could whatever is going on there be the source of the on and off again shudder (forward and back not oscillation) of the front forks at 60 mph up. (You can possibly do this job in a home shop environment.
THe bearings are sealed ball bearings.
There is a spacer tube between the bearings.
They can get damaged and worn in normal use and age.
Rather than a hammer, try a long threaded rod and flat plates to crank them in and avoid ruining them by the forceful pounding of the balls on the races. don't forget the spacer tube...
The head shake is just as likely to be from the "tail wagging the dog".....the rear wheel out of balance or being out of true.
Then the front shakes when the resonant frequency of the frame/wheels will then cause the front wheel/bike to shake usually on deceleration and at the same wheel rotation speed.
For this reason I feel a commando requires extra good wheel/tire components....because of the isos....)