350 UCEs are all carb'd. And I would hazard a guess the tanks would fit on the older frame, having owned both a 350 UCE and a 350 cast iron, but I can't really say. They sure look the same.
This isn't always the best place to ask about the 350 UCEs since they're not sold in North America. (And it's really confusing, in that North Americans generally call the older cast iron bikes "classic" and the new retro-style bikes the "C5", whereas the new retro-style bikes are the "classic" model line in Asia...)
Team BHP may be a place to answer the question, or a local parts shop...