I'm a bit puzzled by the AO regulator, because while most of the companies making electronic regulators make a 12 version for true 12V dynamos (which includes 6V ones which have had special 12V coils or coils and armatures installed) and 6-12 converters which let the output rise to 12V while restricting the field to 6V, the AO appears to be just a regular 12V regulator, which they tell you its OK to use on a 6V dynamo without any mods.
The first generation of 6-12 converters had a lot of trouble burning out field coils because most of them cheated, and ran the field coil at, say, 8V instead of 6V (all voltages given are nominal), in order to get reasonable output at lower rpms. But running a 6V coil on 12V does not seem wise.
Oh, one other thing. While its useful to know that the AO will fit in a Miller box with a little fin bending, those fins are there for a reason - to cool the components inside! Which they cannot do as effectively if the are bend and then enclosed so they are out of any airflow. Once again, I'm not sure how important this is, but is is something to be aware of.