There is at least one other fragment of an LXX MS - found among the Dead Sea Scrolls, catalogued as 4Q LXX Lev [a] which in fact does not contain the Hebrew name. It uses "Kurios". Also dated to the 1CAD it may be older than the Fouad 266, by at least a generation.
Just for my own clarification, can you document that "kurios" is used in 4Q LXX Lev(A)? I had thought blank spaces were left where the tetra appeared in the Hebrew , not "kurios". I could be wrong.
Narkissos, I will look for the reference from Tov, if my memory serves me correct it was in his The Greek Minor Prophets Scroll from Navar Hever. I believe he challenges Pietersma's assertion based on the dative. But I should be more careful citing him till I read his comments again...