I only know that they were famous for having nothing to do with the advertised films.
You might like a browse through this list I've found: http://conancompletist.com/darkofthesun/McCarthy_the_list.htmlI've been trying some random Googling to uncover the artist of those Once Upon A Time In The West images I was talking about the other day and came across that link. Well, a sub-page really. The main site is just Conan stuff and doesn't suggest any obvious relation to Frank McCarthy and his posters, but still, there it is! I've emailed them to see what they know, but I suspect McCarthy is the man responsible. Some of his other work is stunning as well, just look at the one for Where Eagles Dare.