OK, however while Chiang could offer airbases to the Allies, supplying them would be a major issue with the communists (as opposed the Japanese) interfering with land supply routes. OTL supplying American air efforts over the hump was more trouble than it was worth. perhaps the best description of Chiang as an ally against the USSR in this scenario would be a repeat of the German feeling that being allied to the Autro-Hungarian Empire was like being shackled to a corpse.
1. Having the IJA fight "alongside" the US/Allies in China will go over as well as the "new" Wehrmacht helping out in Poland. All of the Japanese troops would eventually (actually quickly) need to be re-equipped with American weapons as the factories that supplied weapons and ammunition in Japan have been trashed. The Kwantung Army, even when it was filled with good troops, not the sweepings that were left in 1945, was NOT effective against mechanized/armored Soviet formations.
In 1945?The Kwantung Army had its own mechanized units in those days, an organic air force, and a large amount of artillery - including powerful fortress guns in Maginot Line-type emplacements near the eastern borders. In training and equipment, it was the best of the Japanese armies and was as relatively well-provided with vehicles as the three Soviet fronts that attacked Berlin in April 1945: 1 truck per 25 men.
1. Having the IJA fight "alongside" the US/Allies in China will go over as well as the "new" Wehrmacht helping out in Poland. All of the Japanese troops would eventually (actually quickly) need to be re-equipped with American weapons as the factories that supplied weapons and ammunition in Japan have been trashed. The Kwantung Army, even when it was filled with good troops, not the sweepings that were left in 1945, was NOT effective against mechanized/armored Soviet formations.
2. Ask yourself, will Chiang commit his best trained and equipped troops to fight the Soviets, or will he prefer to use these to do his best to eliminate Mao and the local communists. Once you come up with the correct answer, how effective will the troops potentially used against the USSR be - and here also, they will need to be armed and fed by the USA with innumerable sticky fingers reaching out at every point along a long supply line from Burma or the Chinese coast to the front. Finally I, for one, would not want to be the US commander with a Chinese unit on my flank hoping their command structure follows the orders/plan and is where they are supposed to be when they are supposed to be.
By 1945 the shipping to get troops to Manchuria/Korea is not a problem. The Soviet submarine threat in the Atlantic will be very small compared to the U-boats even at the end of the war, and the submarine threat from the Soviet Pacific Fleet even less. The limiting factor will be how many troops are available, not the means to get them there.
@ lionhead: I am not being passive aggressive. In terms of the IJA troops operating on the flanks, having non-German troops do this did not work out well for the Germans in Russia in most cases. The quality of the IJA troops in China, both personnel and materiel by mid-1945 is overall poor with obvious exceptions. As far as "backup", basically meaning line of communication troops - God help us. The behavior of the IJA towards the Chinese for the last 10-12 years in China has been atrocious (same root as atrocity). The locals may not be enthusiastic about Americans (or they may be) but the attitude towards the Japanese is going to be universally "unfriendly". I can only imagine what happens the first time some Japanese rear area unit catches some villager getting sticky fingers with a case of K-rations, let alone if some local communist takes some pot shots at them. We know what their response was before now, and I doubt the average unit will change behavior before enough of these incidents cause more headaches for the Americans opening up room for the communists to make more converts ("see, the Americans are simply taking over for the Japanese and using the hated Japanese to perpetrate more crimes against the Chinese people").
Since we agree that the best equipped and trained (and reliable) Chinese troops will be used against Mao et al, the troops that would be "assisting" the Americans would be the lower half - and in the Chinese Army of 1945 the lower half was quite low indeed. The individual Chinese soldier had many good qualities, however in units with rampant corruption, incompetent (but reliable) and venal officers, and poor equipment their utility even for line of communication duties is limited. In some cases better than nothing, in others worse than nothing. I agree that LL/grants to China will massively increase, however extreme measures need to be taken to ensure stuff goes where it is supposed to without massive "leakage", and the troops and especially officers will need a good deal of training. A year to do this is optimistic.
In terms of "troops for Korea and Manchuria", why? If the Western Allies are fighting the USSR Manchuria is a backwater. Korea has some importance in terms of keeping Soviet aviation away from Japan where the US will be building up, but in reality US/Allied logistics for Korea are actually better than those for the USSR. The Soviet Far East has minimal military industry, almost everything has to come from European Russia over the TSRR which is going to be getting attacked with regularity. If you think Russia can trade space for time to absorb an attacker in the west, in the east in 1945 there is a "whole lot a nothin'" the Russians can afford to cede to the USA - if Russia wins, they'll get it back, if they lose it does not matter. Also, as you conceded, American/Allied naval absolute dominance in the Pacific means that they can seize any Russian islands they want, and the whole Pacific coast is at risk for bombardment and raids. Much more sensible use of troops that going through Manchuria.
Would be smart for the Japanese, if they hadn't surrendered yet, to surrender then to the Allies and join them in fighting the Soviet Union, you know, once the Allies take it over from them in Manchuria. Then add the Chinese, presto. Irkutsk here we come(i know, not realistic).
The Americans themselves can make sure the LL will be despersed properly. A year is probably optimistic for attacking the USSR, but not to defeat Mao.