It appears this may never happen. There is a new extra feature in the blu-ray edition of "Cleopatra" (I got the Japanese import this week) on the film's lost footage in which a member of the Fox archives dept thinks the footage cut from the 5+ hour version that Mankiewicz prepared was discarded in the late 70's when the studio cleaned out its archive. The feature also mentions that there is rumour of an approx. 8 hour Black & White workprint version of the film that may have been in the posession of a collector, but they were not able to locate it.
While the archivist hopes the footage may be out there somewhere, it looks like the trail for the footage to recreate Mankiewicz's original vision of two seperate films is getting cold and he feels the longest version of "Cleopatra" we are ever going to get is the 4 hr 6 min roadshow version from the NYC premiere on the blu-ray.
As a fan of the film this is a major dissapointment, I for one always wanted to see the expanded version of the Marc Antony portion of the film which I always felt was choppy and rushed in the roadshow version of the film.
BTW the picture on the blu-ray is out standing- i have only had a chance to watch Cleopatra 's entrance into the Roman forum