This is an interesting document from the National Archives. It's a 1959 US Army document. Note the name Jack Rubenstein. #119-100031-0172

Update: Greg Parker has made the following comment on this document:

I personally don't believe the person named here is Ruby.

There are two better prospects with the same name; both NYC residents. First was head of the Textile Workers Union who had been once head of the Young Communist League. Congressman Martin Dies wanted this guy produced as proof he wasn't the guy languishing in a Dallas jail for the murder of Oswald. An FBI informant told of a party held by National States Rights Party member, Oren Potito. Potito told the gathering that Ruby's real name was Rubenstein and he had been a Communist Party member since 1929. Again, this is a description of the NYC unionist - not Ruby. The unionist was only 6 years older, and did bear a passing resemblance, however...

Revilo Oliver likewise tried to convince his readership that Ruby was in fact the NYC unionist.I believe this was part of an orchestrated campaign to "prove" a communist conspiracy.

The other candidate is described in a book called Counterpoint: The Journey of a Music Man. This JR was a Warrant Officer during WWII Europe. (692 2nd Air Force band). Apparently very unpopular, he was sent back to the States because "he created serious problems for a lot of people" and was discharged. He then became a violinist with various chamber orchestras around NYC.FWIW, I think the Muncie JR (see testimony of George Fehrenbach) was also more likley the NYC unionist...

And an anonymous commenter added this:

The list also contains another interesting entry-Samuel Cummings- an arms dealer who did business under the name of Cummings International Armament(CIA). He started business by importing German helmets from WWII and then purchasing large quantities of WWII weapons and selling them through his US outlet in Alexandria,VA. The CIA reportedly used him to furnish arms to countries who were in revolt in the 50's. He & the agency had a falling out and he lived & died in exile in Switzerland. A remanant of his compny still is along the Alexandria,VA waterfront. He may have importted and sold the Carcano rifle attributed to Oswald.

Update: Jim Root made the following comment about this document on John Simkin's forum:

Interesting document that is dated within days of Oswald's entry into the Soviet Union via Helsinki. The New York connection to Ruby is also of interest because that is where Jack Ruby/Rubenstein countinued his relationship with Virginia Belasco whom Ruby's sister would contact just days before the assassination of JFK and whose family can be associated to Edwin Walker's family as well.