Based on previous drawings, and a couple of wild guesses, I think that the people seated around the table are, clockwise from Spence: Leo Harris, Carmen Maxwell, Joe Barbera, Michael Lah, a generous Bill Hanna (maybe) and Harvey Eisenberg.
A matchbook from Edwards' restaurant, currently available on ebay.
I suspect this cartoon has something to do with how the artist's were made to feel when they took their union break. The ubiquitous Mr. Leo Harris and a couple of other suits wither the storyman Milt Schaffer, possibly TonyRivera or Tony Pabian, effects artist Bob Bemiller and Lovell Norman. "Al" could be Al Grandmain.
The intimidating Mr. Harris hasn't left much of a historical trail. He isn't mentioned in either Joe Barbera's or Bill Hanna's memoirs. His appearances in the cartoon diary may be all that's left of him. He appears to have been a production bean counter and Quimby's bad cop on the floor of the studio.
I don't recall ever seeing an animation credit for Tom MacDonald on a Tom and Jerry cartoon. He might have been an assistant at MGM. He did get an animator's credit at UPA years later, working under Pete Burness' direction on some Mr. Magoo cartoons.
Rough animation by Tom MacDonald for a UPA Mr. Magoo short.
A Magoo short with some Tom MacDonald animation.
Bud Crabbe didn't leave much of an internet footprint either. His son, the cinematographer James Crabe, was also an accomplished magician in his youth known as "Aubrey." One of his illusions was "The Disembodied Princess." It utilized a cabinet which "Aubrey" had built in shop class and had been painted by his father. The cabinet is now in the collection of Paul Osborne and can be seen on his blog*. So, there is at least this one example of Bud Crabbe's artwork online.
The cabinet can also be seen in use in this video.
Who the third vanishing animator is has been lost to binding of the original folio of Spence's diary. *This blog also says that Bud Crabbe was an animator at Disney and Walter Lantz.
A chapter from "The Republic" by Charles Beard. Tito by Stoyan Pribichevich. Photo essay - Kansas. Earl Carroll's lavish show, including photos of Marietta Elliott, Marian Kerrigan, Grace and Nicco, Beryl Wallace and Pinky Lee. Air Evacuation of Wounded. Neat group of photos of different events in Madison Square Garden. The Battle of Baltimore by A.B.C. Whipple. Lucille Ball at the President's ball. War in Italy, photos include pilot Michael Strok, ruins of San Pietro. Full page photo of Britain's Squanderbug. William Allen White 1868-1944. Nice full page movie poster for "A guy named Joe" starring Spencer Tracy and Irene Dunne. Neat full page photo of Air Evacuation, inside ambulance plane, nurse Anne Marie Baran. Individual photos of wounded men, including Myron Whitney, Dale Hitzman, Eugene Pairis, John Lunn, Morris Milner, Floyd Wrich, Henry Wheeler, Theodore Haut, Robert McElheny, Harris Drake, Fred Minch and others. Very nice full page color Coca-Cola ad on battleship. Full page color A & P market ad with Mrs. Katherine Askew and husband John and two little girls.