Are you sure? The version I saw was definitely not 2 hours and 40 minutes long. It was 2 hours and 20 something odd minutes.
I mean you saw the roadshow version with entrance music, intermission, and exit music. Nobody has seen the longer cut since 1968, except maybe the guys who found the footage in the Warner/MGM vault a few years back.
Keeping my fingers crossed the Kubrick estate consents to letting that out for the 50th anniversary in 2018.