Welcome to the forum, erri_wan! and thank you for the kindness of sharing this rare little gem you have. :)
I didn't at first understand you had the complete film, just the alternate opening. Very interesting, a few questions, how long is this cut? maybe hard to check now due to PAL-speedup. Do you know when they aired this, was it in the late nineties?
I doubt this version is the original '71 US theatrical cut but nevertheless it's a really rare and cool Italian TV-version you have here!