The aircraft wasn't an exact copy of the B-29 but many, if not most, of the differences would not be apparent on a model. So unless you want to get down to the nitty gritty, yeah you could take a B-29 kit and make an early Tu-4.
The Russkies reverse-engineered the Tu-4 from two of the three B-29's that landed more or less intact in the USSR. They had to convert alotta stuff to the metric system such as nuts, bolts and the like, but most of this is not much of an issue when building a model. Another thing they had trouble with which also wouldn't be apparent on a model was the fuel tanks.
Some of the more distinguishable differences that would have to be represented on a model would be the engines (Shvetsov ASh-73TK's) and the defensive armament. (23mm cannon) Other than these things, I can't think of much that would be a whole lot different, visually.
Although, they also had trouble manufacturing the wheels and tires and sent some folks to the US to acquire spares. But I dunno how they eventually worked it all out or if they were able to successfully copy these things. And if they were able to do so, I dunno how much different they were from the originals. They had to have come up with a satisfactory solution, though. After all, they built around 1200 of these birds!
Anyhoo, go
here for more detailed info on the story of the Tu-4.
Here's some more interesting and/or useful links:
Monino Bull - 3 Photos (From Bubbamoosecat's website, I believe)
Tu-4 Bull
Tu-4 Threat to the US (Interesting although of no value to the modeler!)
Chinese AEW Bull Walkaround (This isn't representative of the inital Soviet aircraft; there's many differences as can be seen. Especially the engines. But it's an interesting study, nonetheless.)
There's alot more out there, much of it repetitious. Just do a search on any search engine like Google, Yahoo, Jeeves etc.
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