Probably one needs to clarify the resemblances/differences between "psitivism" and "science." They are linked but do not coincide, and to attempt to identify social theory as a purely positivist science is, I suspect, disastrous. Paul Paolucci has an article in Vol. 11 of Historical Materialism which focuses on the extent to which Marx was positivist. I haven't read it yet, but it looks valuable.
Carrol