Sending B-29 copies against the British unescorted is suicide, so to have any chance of success they'd have to slog through mainland Europe.
Well that wouldn't be much of an issue. The conventional power of balance in Europe at the start of this war is such that American war plans observed that mainland Europe would be all in Soviet hands within the first three months. Post-Cold War scholars, with full access to Soviet and American sources, are even more pessimistic: they project that the Soviets would have been at the Atlantic within weeks.
though it does depend on Sweden siding with the allies.
Well, siding with the Allies and surviving the Soviet invasion long enough for the US to establish forward airbases.
Presumably in an actual shooting war with the Soviets the USAF could have / would have made the needed changes much more quickly and or cut some corners vs what was required in peace time. In any event I suspect the supply of deliverable nuclear weapons is going to be a bigger constraint than air crews and air frames. That being said I do expect that the USAF in a "war emergency" setting could have effectively used the nuclear weapons they had in matter of months not years.
Yeah, this isn't supportable by history at all. Even in WW2, it took the US a year-and-a-half from full-mobilization before it was able to mount a sustained bombing campaign against the Germans and that was with a pre-war partial mobilization of another half-year to act as a launch pad. That's three years of mobilization total. Here, the US is starting from a state of total demobilization. While I can see the changes being implemented sooner, I don't see them taking effect any more rapidly and cutting corners in a system which is already struggling is liable to get people killed rather then improve effectiveness more rapidly.
Your also forgetting another bottleneck: the AEC. The bombs were not kept under military control: they were under control of the civilian Atomic Energy Commission and were only to be released to military control after the bombs had been transported to the airbases and assembled by AEC bomb teams. Just assembling bombs for the testing programs of Crossroads and Sandstone maxed out their capabilities.Eeven the bomb teams they did have were found to be woefully inadequate at assembling their weapons. The issue was so bad that the Atomic Energy Commission privately admitted that they were unable to assemble any of the bombs under wartime conditions. What's worse, the AEC was not on talking grounds with the military: the head of the AEC, David Lilienthal, was deeply suspicious of military personnel and vigorously opposed military influence in atomic decision-making. As a result coordination and communication between the AEC and the military was practically nonexistent. It wasn't until 1949 that the AEC finally got enough trained teams to be regarded as sufficient and 1950 that control of the weapons was moved from AEC to military hands.
Edit to add: presumably the best / most competent / combat proven air crews / ground crews etc from world war 2 could simply have been drafted back into service in a war emergency setting.
They'd still need to be retrained in their roles. Military skills are extremely perishable.
Apart from the radars, aircraft and missiles...
Yes, yes, we know. You are completely unaware that the Soviets in 1948 have aircraft and radars for their air defense systems and think their the sort of
untermenschen Nazi propaganda made them out to be, presumably imagining the Russians to still be pounding rocks together in caves or something. Meanwhile, actual scholars who have bothered to examine Soviet air defenses in this period have found them to be a effective and organized system with the aircraft and radar systems to match as one would expect of a military superpower.
Given the poor state of Soviet air defenses against high altitude bombers like the B-59, B-50 and B-36 I'd expect few losses to MiG-9 and Yak-15's, especially given the poor state of Soviet RADAR systems and the small numbers of high-performance interceptors (and their short ranges and loiter times).
The B-29/50 are eminently interceptable by Soviet systems of the day and not only would the B-36 not be available until 1949 (by which point the Soviets have the MiG-15), but it was something of a white elephant: the 1949-50 variants were maintenance nightmares and their airfield requirements were so high that there were only three airfields in the world capable of supporting them, all three of which were in the Continental US.