I think the only difference between fission and fusion would be the amount of fallout. A pure fission bomb would have proportionally more radioactivity as the unfissled Uranium and Plutonium would be more dangerous than the deuterium.
I don't think there would be much overlap in fission and fusion bombs being the same size though. But you might be able to make a 100kt version of both. Of course all fusion bombs will have a fission core.
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