I think that it is possible to have something along the lines of Thatcherism during the sixties, but it would be so different from in it both in style and in substance that it would not be Thatcherism per se.
Something along the lines of an earlier economic liberalisation of certain sectors of the economy can definitely happen. In fact by doing this in the sixties you would probably butterfly away part of the extremes of the seventies with Union strife and this would lead to a midler, more thoughtful and less ideological "neo liberal movement" on the whole.
A lot of the extremism within Thatcherism, especially the style and the rethoric (Thatcherism was much more about style rather than substance anyways). Had its roots not in the failure of the post war consensus per se, but in the Union strife of the seventies.