"how can you say we have so little in common with them?"
Anti-statism is the conclusion of anarchist and anarcho-capitalists. Perhaps this might seem like a large similarity to some, but not to me. I see a wide chasm between the two because of the reasons both groups have come to this conclusion. Insofar as I can claim to understand both, anarchism rejects the state both because capitalism is dependent on it and because it is inherently oppressive by itself, whereas anarcho-capitalists seem usually to oppose the state because it inhibits their ability to use exploitative economic means (capitalism). Notice the contradictory views of the relationship of the state to capitalism.
Now I don't claim to have a great understanding of libertarianism because I haven't spent a whole lot of time researching it. Thus I accept your critique of the vagueness of my response. Anyone wanting to research classical liberalism can do so. Some founding figures include Jean-Jacques Rousseau, John Locke, David Hume and Adam Smith.
"what fundamentals does anarchism question?"
...the state, state-based economics, hierarchy, authority... do I really need to answer this?
"what do you mean "contaminate" anarchism--can a living changing practice be pure (ie it must first be pure in order to be contaminated, no?)? where have you found pure anarchism, outside of a book?"
Well I certainly wouldn't characterize anarchism as "pure," there are already plenty of unexpurgated authoritarian tendencies. Perhaps I should have put "further contaminate"? Or better yet, avoid the discussion of purity altogether - "mar," "corrupt," "infect," - whichever you prefer.
My assumptions are not as solid as you seem to want to make them: "If we want to convert right-libertarians..." "Overall it seems like..." Pretty qualified language. If your read the Phoenix Class War article you'll notice they take a different tact entirely than what I explored in my initial response. What the relationship should be is still quite an open question, IMO.