I'm involved in my local film society here in Edinburgh. We've been working on programming our next season and one of the themed ideas we came up with was a selection of 70mm films. The films we would be showing are probably the obvious choices, things like 2001: A Space Odyssey and Lawrence of Arabia. But, in browsing giallo posters on Ebay over the years, I've often noticed that a fair number, especially on the Spanish ones, seem to suggest that they were 70mm presentations.
The Bloodstained Butterfly
My Dear Killer
All the Colours of the Dark
Is this the case and, if so, is it 'true' 70mm or just a process that allowed the description to be used but wasn't really the same thing at all as far as quality went, perhaps akin to the widescreen processes often used on Italian westerns a few years earlier.
Again, it would seem unlikely that these films were still available in 70mm and even less likely that they would be viable in terms of getting an audience – it's more that enquiring minds want to know...