I've also been spending too much time on ice cream trucks...
I've been looking into #10, and can report that Eiscafé Venezia in Weener is still in business after 42 years, and that #10 was their first ice cream van in 1972. But not much else of any use.
So I began to think that the vehicle itself might be the clue. I don't know much about these small three-wheel trucks - they are almost unknown on British roads - and I assumed it was a Piaggio Ape, as that was the only one that I had really come across. But a quick look around showed that it wasn't one of those, and a slightly longer look around revealed it to be an Innocenti Lambro (or Lambretta Lambro, if you prefer).
Now, if you Google the single word "lambro", apart from these vehicles, you bring up pictures of naked people cavorting around at a pop festival, and suddenly there's a link to picture #30.
So it seems that in 1975 and 1976 there were two festivals in the Parco Lambro in Milan. I confess I had never heard of them, and they don't even appear in the Wikipedia main article about rock festivals, which lists dozens of them. They were called Festival del Proletariato Giovanile, which I guess translates as something like "festival of working-class youth", and were organised by a magazine called Re Nudo, which I'm afraid I have also never heard of.
So I think the connection is between #10, an Innocenti/Lambretta Lambro, and #30, a pop festival at Parco Lambro, Milan.
