I would be surprised to see a review of Machine Gun in Downbeat at the time - it came out first on the tiny BRO private label, and was reissued by FMP in the early/mid '70s, probably not to much stateside notice. But then, I wasn't there, so I could be wrong. Litweiler took note in his Freedom Principle, which was published in the '80s.
As for Berendt and the European jazz press, well - the music was treated somewhat differently there than here. Somewhat.