I've never actually seen this film so have no personal knowledge of its aspect ratio. And for some reason this site doesn't list the film's a.r., which is unusual.
However, Criterion is very meticulous about the proper presentation of their films, so my assumption is that their 1.66 a.r. would be the correct one. Maybe the print you saw at Film Forum was an altered one; there's no reason it couldn't have been, and on occasion FF has had to resort to alternate prints of films. Just a suggestion, since as I say I have no personal knowledge of the movie's true a.r. and there doesn't seem to be any independent information about it available. But I would bet on Criterion's getting it right.