Well, Bob, I've done the grinding of one Allen wrench (yes, it's 6mm). I was able to remove easily the Nylock bolt quite easily. Then it was impossible to remove the screw because it's head hit the engine before clearing the centre stand.
At first I thought that I could grind or saw off some of the screw to increase clearance, but I'll face the mounting problem with the new screw... So I was looking for a trick ?