50? Make that 100, at least. At the end of ww2, the US controlled something like 2/3 of the world's industrial capacity. If Stalin went full stupid in 1947, expect that figure to hit 80%+ by the time the A-bombs stop falling.
The U.S. didn't have that many weapons in 1947-48. 1948 (EoY) stockpile was 50 weapons, end of 1949 that rose to 170. There was also only a single bomb group, the 509th Composite, that was nuclear capable and just a total of 46 B-29 Silverplates (the version specially modified to carry the Bomb) were ever built. There was not until after the B-50 reached squadron service that a second bomb group was trained in the special delivery profile required to deliver the 1st Generation weapons. Flying from bases in the UK the Silverplate has enough range to reach Moscow, barely. It did NOT have the range to reach the relocated Soviet industrial plants moved further into the Soviet interior. That would require the B-36, and that aircraft was not yet in service, it was 1950 before the B-36 had successfully integrated its very complex defensive armament and allowed the guns to be more than very expensive ballast.
Moscow is also beyond the range of escort fighters (even launching from West Germany, which in a shooting war with the Soviets is contraindicated), much less flying close to the Urals to hit industrial targets. We are all well aware of just how vulnerable heavy bombers were to enemy fighters and the Silverplate only carried tail guns. Add in the fact that the performance envelope of the B-29 makes it virtually impossible to "hide" a Silverplate in a formation of conventional B-29, the breakaway maneuver would, if everyone was lucky, wipe out half the formation.
The Soviets, by mid-1948 also had the MiG-9 jet fighter in squadron service with its 600mph top speed, 42,000' ceiling and one 37mm and two 23mm cannon along with the slightly less capable (and even uglier) YaK-23 jet fighter and the piston engine, but still quite capable La-11. Sending unescorted bombers against them would be late 1943 all over again.
If China grows as fast as Taiwan did iotl, it would be less than 40.
China won't grow that fast. The Soviets will not be able to prop up the CCP against the KTM in this scenario. At best the Chinese Civil War continues well into the early 50s, at worst once the U.S. has sufficient weapons (around 1950) it uses nukes to wipe out what it sees a Soviet client state.
to the OP:
It is probable, not certain, but probable that the West would prevail. While it would be close to impossible to wage a strategic campaign against the Soviet Union, a similar campaign against Soviet bases in Eastern Europe is much more possible, especially with the ability to provide F-80C escort all the way to & from the target along with late model P-51 and P-47N. "Tactical" use of nuclear weapons against Soviet troop concentrations would also be possible, with all the consequences that would entail. The Red Army would have around 4-6 weeks to reach the Channel before the U.S. could transfer sufficient tactical and strategic airpower into the UK to stop them cold.
It is also very questionable if the Soviets wanted to have any part of a war with the West in 1948. The country was still largely in a state of ruins and it is an open question if Moscow could have provided the logistical support necessary for any sort of extended campaign. What Stalin clearly hoped for was the West to simply pick up its ball and go home. When they didn't he backed off.