Bearing in mind that I am not a button or a rivet counter, would the Korean war British in tropical uniform be passable figures for 14th Army in Burma?
Okay, I am assuming later war once they transitioned to the green jungle uniform. There are some slough hat figures in the WW2 range designed, I believe, for the Far East. The jungle hat on the Korean range looks more like a modern bush hat than a slouch hat to me but the norm was helmets in combat except for those Indian troops, whose religion didn't allow it - Sikhs being the example that leaps to mind. 8th Army in long trousers would be a good solution, but I think they are all in shorts. But a bit of putty might fix that. It looks like you might only need support options as the slough hat figures cover the basics.
I hope this helps, do shout if I can do more.
Kind regards,
Richard