I think I've stated before in one of these threads that contrary to what the OP says about the importance of the POD, it is actually critical to the scenario.
You could take it as a straight forward versus: every nation except Britain and Japan become entirely passive, this is known to both, and the two fight it out with what they had OTL in late 1941. In this case, it's pretty simple, while the RN is a lot bigger and can bring all of its strength to bear thanks to magic, it'll get trounced in the open water due to the crappy state of the FAA, and nothing the RN has being optimized for Pacific conditions.
Or you can try for an actual semi-realistic scenario in which case a POD is critically important. (and likely impossible to find) How far along is British rearmament, and what threat triggered it, and what's the state of that threat by the time a war with Japan begins? What exactly is the US doing such that Japan could even consider a war with Britain alone? How did the war begin: is there a sizeable RN element in the far east that is vulnerable to a surprise attack a la Pearl Harbor or Port Arthur? etc, etc.