Well, after much meditation I have decided not to go for gluing the magnets with glue.
I have been looking for more than a week for a magnet rotor with the same reference and in good condition, discovering the greed that show the hoarders of Z1300 parts in Europe with their stratospheric prices for a simple piece of a junked bike.
In the end, thanks to Ebay, I found one in Australia at a fair price including air freight.
In a couple of weeks I should receive it.
Well done. Proper too. Sometimes, I'd like to play with stuff like this. On the bench. Glue magnet piece back on, put on a variable DC rpm controlled motor, observe waveform output on o-scope from each of the 3 AC leads, then look at resultant DC rectifier output signal.