Clarification
G'day Mark,
Start with the gear indicator lever, can you select six indexed positions, eg 1n2 3 4 5 with the gear indicator lever?.
If no then the problem is inside the box itself, either the bevels are incorrectly timed or something is preventing the cam plate turning.
If yes, do you get five gears and a neutral?. If yes then the problem is in the gear selector mechanism under the change cover. Remove the cover and manipulate G66/AS. This should operate G49 to engage a different notch of G43 for each gear.
If you can select six positions with the gear indicator lever but get four neutrals (rear wheel/sprocket free wheels) and two gears (rear wheel/sprocket locks up), then the problem is under the cam plate.
The gear wheels would have to be missing for this one.
Try those and if your still lost, get back to me.
Phelps.