Yeah, I've read the first two scanlations and I got this off /rs/ while waiting for the others. This story is seriously blowing the shit out of my mind.
If anything, the art in this is quite impressive for a 1971 manga. I always thought Go Nagai was a pretty mediocre artist due to the occasional anatomical flaws in Devilman, but the guy had to churn out five chapters a week for five different series back then, which definitely explains a couple of minor errors.
Mao Dante and Violence Jack are proof that he could draw some really impressive stuff without a tight release schedule.