Feels that'd make the Pacific Front a questions of "how quickly can more soldiers & equipment be rushed into Asia" VS "how quickly can Japan overrun European colonies so Britain has to fight its way back in & struggle badly" (esp. as Japan will hope Britain will give up sooner than later if it gets too hard).
Well, the first question is "Does Japan still take over FIC, or attempt to?"
If they do so, then there's an AIF or two sitting around with not much on, up to 2 NZ divisions and several Indian formations that were providing muscle in East Africa, even without GB's contingent. The RN doesn't lose forces to Italian action (Valiant, QE) or indeed to quite so many German interventions in the Med (Crete). Moreover, the bulk of the RN submarine force was, I understand, designed for the Far East but dragged to the Med - where it wasn't best suited - in an attempt to interdict supply runs to Tripoli. Plus, being able to run supplies, men and material through the Med, rather than around the Cape, means demand is far lower. The RAF still needs to defend britain, but there's no Desert Air Force, no losses over Greece. They may be spaffed up the wall in fighter sweeps over the low countries mind.
All things being equal, if the Japanese are allowed into FIC, Britain has far more scope to send men and material to deter further action. This includes commanders with a bit more gumption than those on the ground in OTL. Even if Japan catch them on the hop, they're in a far better position to hold Burma and perhaps the Malay barrier.
If they aren't allowed into FIC, then Japan has two options. Try to interdict the supply lines from Indochina on the ground, or fight their way in. If they're forced into the latter, then all the dice are in the air. They can't go for Malaya and the DEI until they've got the bases of FIC. They can't give the British and Americans too much warning, or they'll be prepared. They can't strike the US Pacific Fleet until the Kido Butai is ready. Discussion on the Old Country has always suggested that Pearl Harbor can't be brought forward by more than about a week.
So does Japan move at all?