I have now checked, by stealing a straight ally gearlever from a C Comet and fitting it onto the prewar Burman in my Meteor, that the the splines are the same. The A appears to have a stud for holding the gear indicator so, even though the splined shaft may be, the indicator shaft is not identical.
The start of all this questioning was my desire for a folding kickstart pedal so, as I was in the area, with spanners and motive, I whipped the fixed K/S off the Meteor and found that its spline was considerably smaller than that of the gear lever. Odd in a way as the kickstart shaft needs much more strength. I can understand that the gear lever shaft is hollow to carry the indicator but that could have been reduced. I had not really expected to be able to interchange gearlever and kickstart but thought a post-war folding kickstart to more easily found than a pre-war.
Next stage was to steal the C kickstart. Not so easy. As is my habit with tight splines, I removed the pinch bolt. I've never been confident that it didn't bind in the groove around the post war spline. I still had to lever the kickstart off as it was tight even once this groove was cleared. The A shaft does not have this groove.
The folding kickstart lever slid onto the Meteor shaft so easily that I'd expect to have to open up the gap to enable more of a pinch if it was intended to stay on. Refitting it on the C took more than just spanners but I was good and used a Thor hammer gently.