On something like a Mini about all you can do is make sure the burrs are level. Attach a dial indicator to the shaft and make sure the outer edge of the lower burr is the same height everywhere, if not rotate it until you find the best alignment or shim it level. Now if you can, do the same thing on the top burr. I say, if you can as it's a lot trickier to measure the top burr's alignment. I don't think there is a way to adjust radial alignment.

Ira