Mike,
The mesh of the indirect gears will not be affected by this shimming as you will only be adjusting the position of the input shaft. If you remove the gear indicator, you should then be able to remove the side plate from the gearbox, leaving the selector quadrant in place. Then you will be able to select each gear and check the mesh of the dogs for 2nd, 3rd and top gear (1st gear cannot be seen as it hides behind the casting). You will probably find top only meshes by about 1/16" - which is not enough. Do not try to make any adjustments to the actual selector forks as this will only result in you losing from 3rd gear what you gain in top. To shim the front bearing, you will need to remove the front plate (figure 8 shape) and remove the coupling. These can be stubborn - if you don't have the use of a special puller, the method I find works well is to undo the nut a couple of turns then keep squeezing the coupling in the vice, moving round 1 spline each time. Eventually it gives up and releases. With the coupling removed, undo the 4 screws on the inside of the cover - you will then be able to withdraw the input shaft and the loose rollers. With the cover warmed, press out the outer bearing track and hardened facing washer. Make up a 1/16" shim to fit behind the facing washer, and then reassemble as before. You will now find the outer track stands proud by the thickness of the shim. Make a 2nd shim to fit around the outer track and to the same shape as the retaining plate. Refit the input shaft and loose rollers - then check that the coupling will still fit on the front of the shaft (you may have to tweak the oil throwers so that they do not rub on the front of the cover plate - in some cases, light machining of the cover may be needed). Refit the front cover and check that top gear can be engaged without the dogs bottoming out.
Whilst doing this, some members have taken the opportunity to do a bit of machining and fit 'a proper oilseal' to the main shaft, but bear in mind that this is the only place the Dragonfly box can 'breathe' as there is no breather in the filler plug (as on the Marks). If other breathing is not provided, oil will find it's way out from any other weak point.
Get back to me if you have any problems.
Regards,
Eddie.