Have a look at the blue GTR a few pics below your one on the thread you quoted above, the P reg one, that's what you need. It's using the smaller plate and smaller sized letters as allowed in the document above, you're allowed a smaller plate to fit the recess. You might be lucky and get all your characters in, although all your characters are "fat", you need a "1" somewhere
Your current one has the wrong thickness of font and the N and M are too close to the edges.