Preventing Gear Selector Over Travel

One major headache with a Cord gearbox is gear selector over travel which results in the release of balls and springs flying about and ending up in a catastrophe.
In the booklet written by Sid Ayres on the Cord Transmission one solution requires careful internal grinding of the selector rings. The modification was written up by John Bamberg on pages 55 and 56.
Another approach pioneered by Harold Allsop in Canada is to centre punch either side of each ball so that the balls are restrained and cannot fly out.
A friend here in Australia suggested tubular sleeves on each of the selector shafts. This idea has merit but the main vacuum cylinder's force would still be on the selector mechanism.
A gate with stops up front on the gear box which the lever on the cross shaft would come up against would allow no further travel of the selector forks once they were in the desired detent locations. No further loading would be applied to the gear selector mechanism inside the gearbox.
I would appreciate any comments on this proposed modification which is designed to save and prolong the lives of our precious gearbox internals.