Well, to answer my own post, ya need to preload the linkage against the play in the linkage (and there's still a little, even though all the bushes are newish).
I pushed the linkage lever in the direction of 1st gear, twisted the relay shaft the other way, to take up the play at the gauge, et voila, perfect adjustment.
Well worth sorting, makes those notchy synchros so much easier to live with.