I would use A. But I wouldn’t go so far as to say that B is incorrect. It sounds odd and old-fashioned to me, but there are examples of "have been long known as" in published books.
You can confirm that if you do a google search with "have been long known as".
Here is an example from a chemistry journal: (https://www.princeton.edu/chemistry/macmillan/publications/Tracy_Orgcat.pdf)
"Oxy-allyl cations have been long known as transient electrophilic species since they were first employed as intermediates in the Favorskii rearrangement in 1894."
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A is correct.
A. These creatures have long been known as our friends.
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