Okay - it's installed. Now the cupboard door above won't close. Not enough clearance. arrrgghhh.
Thinking about it for a moment or two (Rocket went visiting to the paintball field), I loosened the (very long) screw at the top of the microwave and put a shim between cabinet and microwave. Just enough clearance.
But now the other door isn't quite level with the left-hand side door. Adjust, tighten, adjust, tighten.