Granted the Soviets had a good number of aircraft at war's end, but the U.S. had well over two theaters worth of fighters. Unescorted bombing missions weren't anything new to the Americans, either.
As far as the B-29 was concerned, it had a combat range of 3,200 miles (5,230km) and could have easily struck strategic targets in the Soviet Union.
Bear in mind that the U.S. was fully capable of escorted long range bombing missions and new bomber designs were in the works by WWII's end so that if hostilities broke out between the U.S. and U.S.S.R., wartime production would be able to ramp up the production of the later designs like the B-32 and the B-36. The B-32 had a range of 3,000 miles (8,815km) and a ceiling of 35,000 feet (11,000m), the B-36 was capable of about 6,800 miles (10,945km) and a ceiling of 48,000 feet (15,000m).
The Russians didn't focus on strategic bombing, and the Germans never used a solid strategic bombing strategy against them, so thier experience in that regard would put them at a disadvantage. Granted, the Russians had good fighters and experienced pilots, but so did the Americans, who not only had the strategic bombing and high altitude combat experience, but experienced personnel from two different theaters at thier disposal.
Take into consideration that not only were newer and more powerful bombers becoming available, but the U.S. had thousands of heavy bombers on hand, which goes back to the formula for beating Germany with quantity over quality (classic argument of Sherman versus Tiger). I seriously don't believe the Soviet Union was prepared to defend themselves against that type of warfare, and any "wonder weapons" they had scored from the Germans wouldn't have been ready for production by such an early date.