I don't worry about 1.85 films being displayed at 1.78. The difference is minimal, but at 1.78, you're getting a little extra image, but again, not enough extra to wreck havoc with what the filmmakers intended.
But a 1.75 film being projected at 1.78 would require trimming off part of the top...
Interesting in that when WAC announced this, they also announced the 1954 MGM film Athena, which their announcement said was being presented in 1.75. That was the one I was questioning. Thanks (and to Bob Furmanek) for setting that record straight.