So far, I've got the initial 1942 Japanese offensive working very well. A few glitches need to be fixed. Initially, after conquering Burma, the Japanese turned almost entirely against China, and it was impossible to save it, even by using all the B-24s, Wellingtons and other long-range bombers to interdict them. I used moveunit events to fix this, but it's a bit of overkill and I'll still need to balance it.
The stalemate in 1943 seems to occur naturally, which is good. I need to add several key Japanese counter-attacks based on British re-capture of certain cities. And the big Japanese invasion of India (Operation U-GO) in 1944 needs to be added, as does the uprising of the Indian National Army against the British if the Japanese break through.
Some events aren't working yet. The lend-lease events to trigger Chinese reinforcements don't seem to have any effect, so that is a priority. On top of that, Japanese fighters shoot down almost all of the airlifted supplies, so I'm still wondering how to fix that. I added a second set of airports, one in India and one in China to increase the chances of some getting through.
A smaller glitch is that events creating Japanese riverine gunboats don't work. I assume that is because they are ship units that I'm trying to generate on land. ToTPP allows ship units with a special flag to move on rivers. I'd have them appear in a port, but I don't want them sailing off into the ocean instead of up river.
The British air transport stuff works great. Giving transport ships the paratroop flag allows them to jump into Japanese rear areas. I've used 2 types: gliders and C-47s. Gliders go first, and also have the engineer flag. They build an airfield before being disbanded (house rule), and then the C-47s can jump in with reinforcements and jump out again the next turn. Air transport of troops and supplies was used in Burma more than any other theatre.
Several Indian armoured brigades arrive during 1944 and 1945, giving the British powerful offensive capacity. In the last year of the scenario, the British also get a few Royal Marines and some landing craft, as well as 3 battalions of Indian paratroops, giving them all they need for a powerful drive to recapture Rangoon before the end of the scenario.